None...maybe a post workout shake with some whey protein in it. Your only 18 and just starting out, your body doesn't need supplements at this point.
Go to the specific diet and nutrition forum and read up on diet and get that squared away, that is the main thing. Add that to a solid workout routine and you will see ample gains.
Good luck bro and welcome to FT!
Mojo is right....you will have all kinds of companies willing to sell you whatever you want and then some, but you do not need anything at this point. Train hard, eat well, and rest. Repeat this numerous times.