With your budget, look for an AMD processor as it'll be cheaper than Intel. Try to focus on the graphics card since you want to play games, at the expensive of other components. You'll probably also need to go with a hard disk drive over a solid state. If you want to be able to upgrade it in the future, look for a ATX mid or full tower and a ATX motherboard so you have room for future expansion. As far as which parts, do alot of research and make sure all of your parts are compatible with each other. The major thing will be to make sure the motherboard socket type (like LGA 2011, LGA 1155 for intel, etc.) is compatible with the chip you are getting. This information will be displayed pretty prominently. Other than that, with power supplies, graphics cards, hard drives, RAM, and optical drives there typically won't be any compatibility issues. I'd suggest starting with a processor and motherboard and build/add components around that.