Hi - don't be nervous, you'll be bound to find someone like you.
Come to think of it, it's probably good to be nervous, tentative, cautious to begin with. The loud noisy types in Fresher's week have to live up to that, and often can't, and if they can, they are normally annoying and no-one likes them come the second semester. Uni has a massive mix of people. I am pretty plain, as are most others, so I go with the flow, don't mind clubbing occassionally, prefer hanging out and talking... I'd also say you spend *A LOT* of time with other people, which isn't completely my thing - I like to be a bit anti-social at times.
Typically, it's a whole lot friendlier than school. Everyone is really nice, if not a little dull. That said, if you find the people you end up in halls with a bit dull, you can just join the societies - certain types of music, sports (be wary!!), arts, drama. Actually, the obsolete sports like archery (twa-ts), or pool/snooker (yess!!) are often the most chilled out and sociable (rugby is pretty boisterious - if you're 'nervous', don't go here). But it's fun. You learn a lot about yourself. You'll probably get a bit depressed at some point, because it's quite hard living away from your family and friends, and everything's a little bit forced, but remember that many others are just like you. Gregarious types might have a massive friendship group, but anyone can find a few good close friends who they can talk about anything with.
My advice would be: be wild, but not in Fresher's week. Let people know you as your parents/friends back home know you first (kind, nice, easy going, chilled, friendly, quiet)... then start experimenting when you've got friends you're already comfortable with. That is, you've *got* to drink, chuck stuff out of windows, try pathetically and ineffectively to get with girls in clubs. *Don't* spend too much time on facebook, it's literally a waste of time - either do socialising, or education (both your syllabus, and read some clever books and papers and stuff too). Good luck!