How can i tell what computer parts are compatible?

I am trying to build my own Compatible Parts , and im not computer dumb at all. I know how the parts go togeather and all that jaz, and to ground my self so i dont static shock the boards and stuff... but i dont know how to tell whats compatible.



I took two years of computer programing witch you may say "what does that have to do with computer hardware" well my teacher made us ready for our A+ certification. Eather way its i just want to know how to make sure i have Compatible Parts .



Furthermore, to help you out, i am trying to build a gaming system, with atleast 2 gig ram, a nice but not over price graphics card. So any suggestions on what might be good Compatible Parts to get? Also my price limite would be between 1300-1500 dollars