Its actually fairly low-key and most of your time will be spent on Intro classes, library tours and other predictable stuff, and night-time is what you want. Yes some people will get off their faces on a nightly basis and be fit for b-all the next day, but the majority of new students are not total p*ss heads, and the Uni will provide lots of other stuff to do if you are not a party animal or don't drink.
As a minimum of 'going out', aim to go to the Friday Night bash with your flatmates - even if its 'I'll go for an hour' and see how it goes. For every other night there will be plenty of 'other stuff' - film nights, coffee crawls, guided walks, and plenty of other 'silly stuff', promise.