16 in a fwb relationship and don't know what to do.. Help!!?

These are the kind of situations that sound exciting, but generally leads to a guy releasing fertile sperm, and that needs to be done under some control. So, if you two are going to explore, take it seriously enough to limit your activities to touch, and oral. Generally, a couple can stimulate arousal, and orgasms, with her giving him a hj, and he fingering her clitoris. In time, you both can advance to oral stimulation, using your tongues and lips. Lesson of the day is to not allow his ejaculate in your vagina. It really isn't that difficult to control, and it usually is pleasurable.

Why did you get into the fwb relationship in the first place? My guess is that you want intimacy without the strings? If you're just shy because of inexperience then, I hate to break it to you, but everyone starts out inexperienced and the only cure for it is, well, experience. But it sounds more to me that you're not ready for sex and got into something you're not ready for since you were glad you didn't have sex last time and are nervous doing anything more sexual with him than making out. I'd suggest taking a step back and think twice about your situation. Do you see yourself having sex with this guy, sooner or later? If not then best to end things now since sex is sort of the point of fwb relationships.

Judging from your name, I'm guessing that you're a woman, btw? This might sound sexist, but I don't know many women your age that enjoy giving their first time in a non-committal relationship. Yes, I know women can enjoy sex as much as men, but, AFAIK, it's mainly more experienced women that go for fwb relationships. If I didn't tick you off here, then I'd recommend thinking thrice about this.

If you really are not sure what you want you shouldn't be doing anything with him. He has it all figured out what he wants, sex with you without any sort of commitment. In other words, hit it and quit it.