Go to Riverwood. Find an elf named Faendal, and deliver the note to Camilla. Then find Faendal and ask him to follow you. Make sure you have at least least 200 gold. Ask him to train you. When he does, go ask him to trade with you. Go into his inventory and take your money back. You can do this 5 times a level, and it really helps at an early time. You can do this an unlimited amount of times, as long as you have the gold.