Ant, consider yourself blessed to have received such a camera.
However, many people who get big fancy DSLRs without any formal camera knowledge end up frustrated over them, or don't ever use them to their full ability. I strongly suggest you take a photography class at your earliest convenience. Just a basic black and white film class is enough to get the ball rolling.
You should also research your lenses to understand their strengths and limitations. From what I'm reading, your lens produces a lot of chromatic aberration at the 300mm setting, so you may not want to use it there.