Identities

This week in trig, after the test, we briefly and vaguely talked about Pythagorean identities. From what we've learned so far, learning the identities of at least these three equations will make our lives so much easier when we move on to calculus. What I understand at this point is that all an identity is, is the different form a certain question takes on. For instance we could have 5 "different" equations but they would all be asking and answering the same exact thing. I'm hoping to learn more and better understand all about identities before taking AP calculus next year.