I would suggest for anybody with any sort of question involving credit (rebuilding credit, loans, establishing credit, etc.) to go to myfico.com and sign up for the forums there. Lots of your questions will have already been answered there, or you can ask and there's a lot of nice people to help you. The information you can get on there is priceless because credit plays a huge role in your life.
Credit is an amazing thing if you use it wisely. You can't think of a credit card as a way to purchase things you can't afford. Anything you buy with it you need to pay off within a couple of months or else it will hurt your credit. Just use your credit card for purchases you would have otherwise used cash or your debit card to pay for. Then use the cash you would have spent on the purchase to pay off your credit card. If you pay that shit off soon enough you won't accrue any interest on the balance so it won't even cost you extra. You want it to report before you pay it off though so the companies that do the credit scores see that you are using the card and paying it off.
And as Shea said, keep the balance under 20% of the max amount of credit you are given. I've heard 30% was the number, but 20% will help you more anyway so I'll just go with 20%.