trans | A question

I haven't had much experience with transgendered people, and I was wondering what the thinking behind it generally is. I was under the impression that people felt that they were the opposite gender trapped inside the wrong body, e.g. a guy trapped in a woman's body, but I was told that this is actually not that common.

I know the question's vague, and it's probably been asked before - but for the transgendered members of the community, what are the specifics of your being transgendered?