This happens to be a very important part for gaming, it is what will determine you minimum frame per second (FPS) and your maximum FPS and your gpu will fill in the rest. You can always lower the settings in a game to get it to work with a weak gpu but there isn't much you can do about a cpu that is too weak. The i5 6600K is based on Intel's new Architecture, Skylake, and socket, LGA 1151. The i5 6600K has very good performance for gaming. It out performs all of the AMD FX series, even the FX 9590, in all games due the differences in architectures, more cores and ghz don't make always cpu better.
This is what keeps your cpu cool and stops it from frying itself. The i5 6600K doesn't come with one but that is okay since I have selected a aftermarket one. This cooler is slightly better than the Evo 212 by a couple of degrees. As the name implies its a quiet cpu cooler. With this cooler it will allow you to do a decent overclock of the i5 6600K.
This is also a important part of the build. It determines what features you have and can use and if you can overclock your cpu and if it allows you, how high. This motherboard will allow for some decent to good overclocking and it has what I consider decent features.
Ram is just ram when it comes to gaming. There is no noticeable difference between ram speeds when ti comes to gaming. I chose this ram because its priced fairly and it will look good in the build.
This is one of the best 120GB SSD's you can buy right now and it is priced decently. I can't think of anything more to say about this right now.
This is a decent HDD. There is a myth/"study" that goes around saying Seagate drivers are unreliable but its just a myth/poorly done study. I have more info about it in my profile if you are interested. It has a standard speed of 7200RPM.
It has excellent performance, it slightly, only slightly takes the league at 1080P versus the GTX 970 but a league never the less and the gap widens as you increase the resolution, at 4K it is competing with the GTX 980, not the GTX 970. It has 8GB of VRAM which is not needed at all, even for 4K, its just nice to have and brag about if you are into that kind of stuff. Also with it out performing the GTX 970 in most games at 1080P and above on direct x(DX) 11 games, there are a couple of benchmarks out there showing a even wider gap in performance but I wouldn't take them too seriously since its only 2 and its too early to tell and that there are actually no full DX 12 cards on the market. This models runs cool and it has a backplate which will look nice in the case.
I am not looking to debate performance since it never ends well for either party and just takes room up in the comments, if you want to debate this, don't do it here, do in the video card section of the forums
This is a decent budget case and is good for beginners to build in due to being hard to make a messy build and it has a power supply (psu) cover/basement so you can just shove all of the used cables in there. It will be hard to make a bad looking build in the case. The case supports 280MM radiators (rads) and all in one (AIO) coolers which you might be interested in getting later or now if you can afford it.
This is one of the most important parts in the build and is one that you should never cheap out on no matter what your budget is. The Evga G2 is a top of the line psu, it has top of the line performance, I am not going to get in the detials of that since I have a feeling it will confuse more people than it will help, very good build quality. Its quiet and has a zero fan mode and one of the best things about is its 10 year warranty, although you will have to sign up online for it. It has plenty of wattage for this build.
I selected these out because they are quiet, this build is supposed to be a semi quiet build, and move a decent amount of air. You will want to install these fans on the front of the case due to the case coming with no intakes fans.