I'm the same age as you, and I know exactly how you feel. I understand your insecurities, and that intense fear of "not knowing what to do." I was seriously in the same boat as you a year ago.
I was 19 and had never had a boyfriend, never even held hands. I figured it was because of my weight. In part, it probably was, but I also had low self esteem and didn't think I deserved anyone looking the way I did. I'd had a few hopefuls but 3/4 of them ended up being gay (uhhh) and one of them was just weird. I knew I could GET a boyfriend, but I didn't want some loser not doing anything with his life, or someone who treated me bad. I had this irrational fear of making out, because I didn't know how. At all.
I finally met some new friends, a good group of guys who had lots of fun. I actually met them because one of them who I knew invited me to "porn and poker night" in typical male fashion (no alcohol, lots of joking, and it was always the corniest porn they could find, so it wasn't weird lol). I wanted to say no, because I was so shy, but I wanted new friends, so I said yes.
I met my boyfriend there.

I obsessively brushed my teeth before coming, kept body spray in my purse, and ALWAYS did my makeup and hair. Once we started talking, I was terrified. He had no idea what I used to weigh and look like and stuff. Not to mention if he tried anything, I'd just stand there like uhhhh.
When it came down to it, it all came pretty naturally. I wasn't good at anything, by any means, but it's not rocket science. I was scared, but I got over it. And he didn't care. I even gained a bunch of weight back, and he still didn't care.
I guess the moral of my novelish story is that you shouldn't be nervous, because you'll meet a guy that really doesn't care. If he's into you, seriously, he's just as nervous as you. He won't care what you look like now, nor what you looked like then. And most guys don't even really notice that sort of stuff I've found. Like, if you take your shirt off they aren't looking at your stomach they're like "oh my god, boobs boobs boobs boobs boobs maybe she'll let me touch them? I hope so!"
I'm dead serious. So don't worry, when you meet a good one, he'll take you for who you are. Self esteem issues and all.