Basically it is to test knowledge you already have. That way you dont have to sit through a 10 week course to prove your knowledge. There are general and subject exams. Only the subject exams are normally granted credits. The tests are pretty basic, might get you out of some survey classes, but not much more.
Some colleges award credits for CLEP, some dont. Check with your college to find out how its handled - they all dont award credit in the same way. You have to meet certain scores to receive credit. Sometimes a specific dept wont allow testing for credit, although other depts in the same college will.
Colleges dont like CLEP, it cheats them out of tuition, so you may have to push a bit to get info. Most larger colleges will have a CLEP Administrator, check with them.
Luck
Alac