To answer the question, try muscleandfitness.com. They have a very comprehensive archive of articles for beginners and advanced lifters alike, its free to register and most information is free to the public. Since you're so young and therefore still physically and mentally developing, i would suggest just eating right, and concentrating on your lifting technique. Since you're growing into yourself, stay away from supplements other than a good multivitamin and a whey protein. Puberty will supply you with more than enough testosterone and growth hormone, so you dont need more than that. Also, dont get in there and think you have to compete with everyone else in the gym. You're there for yourself, so lift what you are comfortable lifting, but do not be afraid to ask for a spot or advice on a lift. People are usually more than happy to help.