How the heck can I get a girlfriend!?!!? I seriously need some advice.?

I haven't had a girlfriend since 7th freakin grade.... I'm a sopre now.... in high school... and I see like these 10 particular girls that make me melt like a snowman in a desert all the time at school... some of them try to talk to me... I think because like this one girl that I think is very good looking was talking to me today very briefly and she doesn't usually do that.... my main question is: when a girl looks at you does that mean she likes you? Like it was really weird I saw this girl looking at me who I thought hated me and I looked up at her and looked away and then like a minute later I caught her looking at me, but she's one of those girls that I'd never expect to think of me as even remotely attractive(not saying I'm ugly... I'd rate myself at about 7.5 out of ten to be honest, this self ysis is from other's opinions of course.) but yeah I saw her looking at me and it wasn't like the oh I want to kill you because I hate you so much type of look it was the gazing one with the blank face. I guess my real main question is how do you know if a girl likes you when you don't talk to them at all? And how can you start talking to them if you figure you both like each other? Please help I'm a hormonal mess hahahaha... not to say I'm only looking at girls to get laid(I never said that wasn't ONE of my motives ;D) I actually want a decent girlfriend and I read somewhere that you should never settle for someone you don't think to be a 10/10... even though I've refined what my standards actually are.... or in other words I'm in to girls with a nice *** as well as a nice brain... not just the aesthetics. HELP