The Kardashev scale is a method of measuring a civilization's level of technological advancement, based on the amount of energy a civilization is able to utilize. Kardashev himself came up with three levels, but others have since refined the method to account for higher forms of existence. Earth in the 21st century does not yet rate of this scale, our ability to manipulate energy and matter is in it's extreme infancy. We get our energy from dead plants, coal, fossil fuels and maybe the occasional solar panel or even a nuclear fission reaction. However, with recent ideas about using carbon nanotubes to enhance solar energy collection, and the near invention of nuclear fusion capability, coupled with admirable advances in our political and cultural development e.g. the UN, increases in social mobility and the internet, we are only a few centuries, maybe even A century away from becoming a type I civilization:
Type I--- A type I civilization is a planetary civilization. It can harness the equivalent energy output of an entire planet. Type I energy sources would I think simply be more advanced forms of the renewable energy sources we have today, e.g. solar panels could be improved using carbon nano tube technology, and nuclear fission could be replaced by the far more effective nuclear fusion. These clean energy sources could ease the rate of global warming (though not stop it). They also command the fundamental forces of that planet, such as weather. For example, it could beam radio waves into the earth's ionosphere in such a way as to manipulate cloud formations, making it rain in dryer areas like the Sahara desert (areas that will become more and more common as global warming inevitably increases). I think a type I would make considerable advances in computer technology. In terms of processing power, contrary to Moore's law we're actually kinda maxed out now unfortunately, but that's assuming we don't radically alter the way computers process information within the next couple of centuries, e.g. some scientists are talking about hard drives that don't use binary, electromagnetic circuit boards to convey and process information, but the spectrum of light. Light based computers could process far more complex patterns of information, and at the speed of light as well. Significant medical advances could be made with genetic engineering, e.g. cloned organs for organ transplants. This may even have an agricultural impact, cloned flesh possibly replacing the need for livestock, thus allowing for all that plant food normally eaten by the livestock to be eaten by people instead. Manufacturing advances, such as additive manufacturing could significantly ease the strip mining of world resources, meaning a decrease in the destruction of the worlds ecosystems. It is also I think certain that a type I civilization would see dramatic changes in the world's socioeconomic systems. A type I is typically characterized as a diverse, yet unified political entity, possibly a planet wide confederation, with each member state essentially having its own laws but not in contradiction to international law. With unity amongst the world's nations, perhaps we could facilitate less exploitation of poor countries by rich countries; also, with more energy and resources, there will be less competition amongst nations. With planet wide unity, universal advances in education, justice, communication and even entertainment would be more than possible. Type I weapons could also be more advanced, using sonic pulses, lasers and EMPs over bullets and missiles.
Type II--- A type II civilization is an interstellar civilization. It can harness the equivalent energy output of one or more stars. A type II is to us, what we are to people in the 11th century. There are two main ideas for energy sources of type II civilizations. One is combining matter with antimatter. There are three ways to get energy from matter, one is to split the atom (nuclear fission), another is collide the atoms (nuclear fusion) and the third is to annihilate the atoms (matter/antimatter reaction). This is the most efficient way of extracting energy from matter, as 100% of the matter is converted into energy. Another potential energy source is the Dyson Swarm, Dyson Bubble or Dyson Sphere. This expands on the solar panel technology. Solar panels on earth are limited by distance, clouds and other factors. Constructing a swarm of solar collecting machines around a star would increase the energy collection immensely. A step up would be to create a bubble of trillions of these devices to surround the star. Finally, 100% of the star's light energy output could be collected with a Sphere, essentially a gargantuan spherical internal solar panel meant to completely encapsulate the star (this could take thousands of years even with type II architectural abilities, but then, medieval cathedrals took centuries and that didn't stop them). I think that just as we have made massive advances since the 11th century in terms of world understanding, ethics and even language, the culture of a type II would be overwhelming, just as an 11th century peasant would no doubt be overwhelmed were he/she to see the world of today. A type II would have a much higher understanding of cosmology and physics. A vast majority of matter and energy in the universe we call 'dark', by virtue of us not understanding what it is, a type II would know all about what dark matter and energy are, and possibly even how to manipulate them. Type II ethics may be considerably more advanced as well. I'd imagine that whilst same sex marriage is a major controversy to most people today, it would be the most normal thing in the world for the type IIs. Ethical freedom may be extended far beyond that, extending to machines perhaps, some of whom, by the type II era, are becoming fully sentient. Computer programs in general, may reach a state of consciousness rivalling or even surpassing our own, leading the worlds to accommodate a new race of beings, with all the rights & privileges of organic life forms, and with all their laws applied to them. An interstellar civilization would also need a means of travelling faster than light, as light takes years to get from star to star, making interstellar trade and communication impossible without it. With energy sources like anti-matter and dyson spheres, starships powerful enough to warp spacetime could be built to shorten the trip. Type II would also need a means of colonizing these planets, most of which will be far from earth's habitable environment. The easiest way would be to build biodomes, but some nearly earthlike planets (like Mars) could be terraformed over hundreds of years. Construction techniques would need to improve dramatically to do this. One option might be to dissolve matter into subatomic particles, and then use magnetic fields to rearrange the particles into the physical object you desire. Using this technique, one could even teleport objects from one location to another, by dissolving the object in one location and using quantum entanglement to beam the information to a location and then reconstruct the object there. Entertainment would take on leaps and bounds as well. I'd imagine something as primitive as television would be obsolete in a world of advanced holographics, creating 3-d virtual worlds for us to enjoy. They're weapons would be terrifying, using antimatter explosions billions of times more powerful than nuclear weapons of today in conjunction with particle beams and other directed energy weapons. Also, powerful plasma or energy shields to defend against them.
Type III--- This is probably my favourite one. A type III civilization is an intergalactic civilization. It is to us what we are to prehistoric man. It can harness the equivalent energy output of an entire galaxy. Energy sources for such a civilization is a tricky business. One way could be to tap into the energy of black holes that reside at the center of most galaxies and quasars. Perhaps they could manipulate a black hole to pull in the galaxy's matter and energy at one end, and then spit it out the other so that it could be collected, combined with antimatter, and converted into pure energy rather than being crushed into a singularity where it's of use to nobody. This energy could then be used to both power, and distribute, by using it to create a network of wormholes throughout the galaxy. Another option would be to power space-craft using quantum singularities (like those at the center of black holes), which are essentially infinite in power, but which, I imagine, would be tricky to harness, but perhaps not impossible for a type III. Keep in mind here that type III may use technology in a completely different way to us. Today we use mechanical devices powered by electricity or combustion engines. Type III may be far more advanced, perhaps even using devices made purely out of energy e.g. holograms. I think the most significant aspect of a type III, however, would be the people themselves. Life itself would be barely recognizable at this stage, humans having merged with the technology itself (transhumanism). Human beings would essentially no longer exist, having long ago either become cyborgs, or even transferring their thoughts into android bodies, or holographic projections. These transhumans would spend a great deal of time in virtual worlds, created by neuroactive simulations in their 'brains'. Minds may even be networked in a manner similar to today's internet, but in this case a telepathic link allowing information, emotions and experiences to be shared. Transhumans could 'log in' to this network and absorb information instantaneously. Using such neural interfaces could also allow these transhumans to control machines with their thoughts. The real world would hold great interest to many for posterity, or just because it's friggin real, and thus they would still explore it. A type III has spectacular construction abilities, able to terraform whole planets in just a few years or even months, and have incredible control over space time, perhaps even the ability to travel in time. If type III could time travel, then they may spend a lot of their time in the real world, studying the history of the universe first hand. It is therefore possible that we have met type III individuals already, but we would never know it, as they would no doubt disguise themselves perfectly, also, it's possible that there is a law of causality which allows them to interact with us, but not in a way that changes history. It's possible that they are even the cause of certain historical events, not that we'd have any way of knowing. Type III would be extremely close to fully understanding the universe, and how it works. It is unlikely type IIIs would even need weapons, but if they did, they would defy comprehension, weapons able to wipe out entire galaxies, perhaps by creating a star with a ridiculously short life and then detonating it in a gigantic supernova. They may even be able to defend against such weapons, e.g. creating a black hole at the center of the nova to cancel out the explosion with an implosion (totally ripped that off doctor who).
Types IV/V--- A type IV civilization is an inter-dimensional civilization. It can travel to, or even create alternate realities and use their entire power output. It would be to us what we are to insects, vast and beyond comprehension. Type IV would have a complete and and thorough understanding of how the universe began, works, and maybe even how to duplicate it. It is extremely unclear at this point, what the limits or nature of such a civilization would be. An alternate reality i.e. a parallel universe, may not obey the same laws of physics that our own universe does. If a universe was created by a civilization, however, perhaps a post type III going to the next level, then it is likely they would engineer those laws of physics to suit their own needs. As such, their abilities would likely be godlike, devoid of practical limits (in their universe at least, probably not in ours). A type V civilization can only be described as a multiversal civilization (as opposed to a universal), & would be to us what we are to micro organisms, impossible for us to even imagine. Type V creates multiple universes at will, and can harness the energy of any and/or all of them, and is basically without any conceivable limits, as close to 'god' as is philosophically conceivable to get.
Type n and Type ∞--- According to some mathematical theory, however, there is no limit to how powerful a civilisation may become. Type n highlights this concept, allowing for any number of orders of magnitude by which a civilisation may advance itself. Type ∞, is by definition an infinite civilisation. It can harness an infinite amount of power, consists of an infinite amount of people, controls an infinite number of universes and is for all intents and purposes, infinite.