Also the beauty (well some would say it can be annoying at times, but if you're shy I think it helps) of the Cambridge college system is the group of people on your course is a lot smaller to begin with, and your college might start things off by taking you for meals in freshers' week with your subject group. Later in lectures you can meet other people, but it did help me knowing there was a small group to make friends with to start with. (My best friends are on my course in my college) Also you will be living with other freshers (I would imagine this will be the case in most places, even if you don't end up in Cam), so they will also be looking to make friends. There are lots of shy people, so please don't worry too much, not everyone is super-confident, but I think the vast majority of people find friends, even if it takes a few weeks to settle properly.