Anyone is allowed to receive and listen to signals being broadcast, but as described in the What is Amateur Radio page it is necessary to get a license before transmitting. The short test (26 multiple choice questions) covers the basic skills and rules covering operating a radio system.
CUARS organizes a learning session once a semester covering the core material of the Foundation license. This is followed by two hands on sessions where practical excersises introduce the main concepts of electrical circuits, radio waves, and practical use of a transceiver. After these we run an exam at the university and you're set to take part in all the society activities as well as the numerous activities possible as an individual and with people and groups across the UK and world.
For information on the licensing process and materials covered check out these pages:
The Chelmsford Amateur Radio Society have a complete set of presentations and training resources for Foundation, Intermediate and Full licenses. Essex Ham has slides, revision materials, and videos for the Foundation license.
We recommend Radio Tutor as a great site for checking your knowledge using practice exams.