UCAS
The Universities and Colleges Admissions Service is the obvious place to start for information about applying to Higher Education. Use this link if you want to visit the UCAS site.
The main feature of the site is a searchable subject database listing every course offered by U.K. Universities, their entry requirements and so forth. The site also contains other bits and pieces (maps, access-course databases, etc.) designed to help you choose the right course and University.
For basic information about how to apply and what to apply for, this should be your first port of call...