1) What should I do about this?
2) How can I be more confident around girls, and have something to say all the time?
There's all the self-help stuff about believing in yourself, building confidence, etc. But it's quite pointless as its too general. So here's some concrete "exercises" you should do. For instance, start by walking down the high street, into cafes and shopping malls, and say "hi" to girls. Around 10% will respond with something more, and take it from there. For the second stage of your social self-improvement, use the lamest, stalest chat up lines you know (of the **** if I'm wrong but havent we met b4 variety), because that which doesnt kill you makes you stronger, and rejection doesnt kill (usually). Just say "Do you wanna ****", and you'll get a non-negative response from around 5%. Become used to humiliation. Thirdly, after these "exercises" you'll find your confidence in all social situations has gone up dramatically. Hope this is more useful than those lameass responses like "believe in urself" etc.
3) How can I meet more people outside school (guys and girls)? I mean I cant go to clubs or many places where you can go when you are 18 and I really dont want to get drunk. There arent many people around where I live my age.
You could get a false ID. Alternatively, depending on how u look u can sometimes pass anyway, especially early on and at less classy establishments, further from the city centre. Also, making friends from the local uni or polytechnic and going with them increases chances dramatically. Don't get drunk, 1 or 2 units is ideal to "lubricating" your social skills as I call it. Also NEVER, ever buy drinks to girls ur planning on chatting up.
Alternatively, just set aside half a day and browse thru the coffee shops and book stores (best places IMO) and just strike up convos. "hi" "how do you do" etc doesnt have to be mindblowingly clever, and if u fail to continue well theres millions more ppl out there.
4) How I can imporve my sense of hunour?
Remember that sarcasm is usually a suitable substitute. Apart from that, take the effort to memorize a few dozen jokes. You can find them easily enough on the Web. If your not a 'natural' kind of joky person, it is quite possible to paste over that gap doing this thing.