Start reading bro... you are on an awesome site, Check out the other forums as they are great resources.
Dont mess with gear bro, put it simple you can destroy your body.
At your age your have enough test in your body a bullet would bounce of you.
Learn to workout and eat like a pro first then put some years on from there if you want to try gear LEARN before you put one thing in your body.
Take care
BigGuyPHX
18 is way to young, thats what most on the site will tell you.
Read, Research, you'll get lots of information & knowledge from this site.
Keep training hard, and wait until your over the age of 21.