Welcome, Caroline!
Lots of good advice. For a beginner, I'd re-iterate two, no three, points already made above.
Pat said "aerobic exercise as many days out of the week as you can." Put a different way, be consistant. It doesn't have to hurt or make you out-of-breath, just get out there. Easy ways are to integrate it into daily activities... a trip to the post office for stamps, corner store for bread, whatever.
And, like dnvr said, be sure to have fun... if it stops being fun, rest, recover, and listen to your body.
Finally, stick around! Keep asking questions as they come up!