How is "boyfriend" different than friend? Please just give me the real difference.?

I have a bit of a complicated question that requires a little background, but I need an answer as I am currently at a crossroad and I don't know what to do. I'm an 18 year old male that just graduated 1st in my high school class and now I'm enjoying a relaxing summer. Over the years, I have developed a no-relationship policy to keep myself focused on academics. Anyway, I'm not the best at detecting when a girl is flirting with me, and from what I understand, flirtation is a sign that that individual likes you. Well, about a year ago, apparently there was a girl that started flirting and "crushing" on me. I didn't notice until she got really obvious with her flirtations. I suspected that it was just silly high school love that would die off in a month or some kind of hormonal imbalance that was directed at any male within proximity. But these obvious flirtations continued, till the present. Of course, my friends caught on and now they are encouraging me to date her. She has even suggested that we should "step up the relationship," most likely to the boyfriend/girlfriend stage. First of all, I've never been there, so I don't know what to expect. Secondly, she is an attractive girl and... aggressive? when it comes to getting what she wants. (first time I've ever grinded at a dance was with her, and totally initiated by her) Anyway, my friends keep saying things about her anatomy and her personality that suggests that if I were to get in a bf/gf relationship, it would get more intimate than I would like. I can't figure out if they are joking or not, and I'm a horrible judge of these things, so my question is, what exactly does the status of Boyfriend mean? How is it any different than being a friend and what would she expect from me if we moved onto that stage. In other-words, what more does she want in our relationship? Also, is there some kind of secret social protocol that requires couples who are dating to get sexually involved (maybe not a home run but at least second base http://xkcd.com/540/ if you need clarification), because I've realized this year that nearly all my friends, all at the top of the class, are involved with mutual sexual satisfaction in their relationships. All my life I've been told to be good and suppress my she wolf, but now it seems society wants me to let her out. I hope you can help me, currently I have about 1 week and a half before anything major can happen because she is off in another country for a visit, so I'm safe. Can't wait to hear your response.