I play soccer but i dont know...?

ok i have played soccer a few years now but i have always only played keeper so i was just wondering what is off sides? this year im on varsity. i have a strong felling my stupid cauch, who i hate 4 doing this, is going to play me on the feild also. i dont want to look like an idei or stupid 4 not knowing what off sides is.PLEASE HELP ME!!!