When my parents tell me something I just get the urge to do opposite of what they say. I don't know why, is that just part of being a teenager?

Definitely, but when you act on those urges, you can get yourself into trouble.

It is all part of growing up, one of the developmental stages individuals go through in order to become adults. It's like when you were two and said "No!" a lot and wanted to do things your way, not Mom's way. Now it's happening again, but like teacherjenn said, be careful you don't get yourself into trouble. There are bad and harmful ways to rebel and there are positive ways.

If you are interested in psychology, look up Separation and Individuation. The doctor who wrote about this was Margaret Mahler.

Yes, part of growing up, maturing is knowing when to rebel and when to listen