Go along to some society events and if you're living on campus try to get to know your flatmates - my flat spent quite a few evenings in the first week playing cards.
There's definitely no compulsion to drink - I'm not sure I even ended up in a drinking scenario in freshers? (I wasn't exactly going along to the hard-clubbing socs mind - but they mostly all run sober socials).
Most of my friends I've met through socs or other friends (none met via my course, only friends-of-friends who happen to be on my course), so make friends with extroverts and steal their friends!
If you're nervous/terrified, most other people are too. The first few weeks may be kind of socially messy and draining, but as long as you put yourself out there a bit (it doesn't have to be much - I spent plenty of time hiding in my room!) once first term is under way you'll likely have a group of friends beginning to coalesce around you.
I guess try to go into it like it'll all work out alright, and chances are it will.