Once you've completed all the work, you still won't be awarded the degree until an official ceremony known in Cambridge as a Congregation takes place in the Senate House. The ceremony, which involves gown wearing, finger holding and other people talking in Latin, is always popular with family and friends, although you can get your degree in absence if you have already left Cambridge. Your college will send you the relevant paperwork and instructions when the time comes. The actual degree certificate is rather unimpressive, but for £20 you can buy a much nicer version to keep your relatives happy.
There are several dates throughout the year on which degrees can be collected in person. Graduands for first (undergraduate) degrees usually graduate together in the June ceremony, General Admission; most graduate degrees are collected on other dates. Graduands are presented by colleges: not every college is present in every ceremony, and the precise date and place in the running order is determined by the age and status of the college. Please refer to the online list of degree ceremony dates, and for college-specific information contact your college praelector or tutors.