To add just a little to allaroundhunter's advice, I will pass along that which was told me me when I shot my first (& only, so far) IDPA match: Go slow. Be safe. Speed will come with time.
At the 3-gun match that I shot, there was actually a guy from Louisiana who got DQ'd on the first stage. He set his rifle down on the bench, with a round in the chamber and the safety off. That was it. Done for the day. I will say, though, that he was an awfully good sport, though, and actually loaned me magazines to use for the rest of the day.
A gunfight is not the time to learn new skills.
If you ever have a real need for more than a couple of magazines, your problem is not a shortage of magazines. It's a shortage of people on your side of the argument. -- Art Eatman