There are books you can read for this. Real Time Collision Detection by Christer Ericson is fantastic, for example.
http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604
If you don't understand the math in that link, drop your project for a while, and do some real math reading. If you don't know basic linear algebra, cross products, dot products, how basic matrix multiplication works, and how to project vertices onto a line/plane, find distance between vertex and a line/plane, you will need to before long.
Christer Ericson's aforementioned book goes in assuming that you know very little math, which is great. It's pretty easy to find and pirate.