Advocated means plead the cause of... argued for the side of whatever the person is advocating. If you are in a class where the teacher accuses you of cheating, and the person behind you stands up and says no way... I was here, and I know that person did not cheat, then that person is advocating for you. If you hire a lawyer, you are hiring the lawyer to be your advocate in the legal system... to be on your side and to stand up for you and fight for your position.
To speak on behalf of, or in favour of, something or someone who is not able or willing to do so for themselves.