There's a few things that go into a PC build. You need to be comfortable working with electronic components, some of which are very sensitive to static electricity; its not a huge problem but there is the CHANCE that you could fry something.
Having said that, Tom's Hardware does a good job of putting together PC builds at different price points:
http://www.tomshardware.com/reviews/best-pc-builds,4390.html You could simply get all of the components they list in the build that's closest to your budget.
Note that none of the builds include a monitor, keyboard, mouse or Windows license - if this is your first PC build, you'll have to buy those things. Windows runs about $100, and you can get a keyboard and mouse for maybe $30 or so, but you may want to spend more if you're going to be gaming.
If you're really on a budget, you might want to look at the new Ryzen processors with integrated graphics - that'd give you acceptable entry-level graphics performance and you wouldn't have to buy a graphics card. If you are, let me know and I could probably cobble together a build for you.
Having said all of that, if you're just looking to get a cheap gaming PC, given how expensive graphics cards are at the moment, it may be cheaper to just buy a pre-made desktop. Once you have one, you can always change components over time, which is a good way to learn how to build a PC.