During the online Student Registration process before you arrive, you'll complete the account setup process and obtain your email address and university passwords.
There are three accounts normally issued, although you will have the same password for them all:
Hermes: The University email system.
Raven: A university-wide authentication system to access to restricted web pages and resources.
MCS: The password to log in to the computers in College, at the University Information Services and in other Colleges and departments who use the same system. MCS stands for 'Managed Cluster Service'.
Make sure that you log into email regularly before you arrive as you will very likely be receiving important information that way. The quickest way is via Webmail. To configure other email clients such as Outlook or Thunderbird, see here.
Almost all bedrooms and shared areas (libraries, etc) have wifi coverage. You need an Eduroam token to use it. You can get this here: https://tokens.csx.cam.ac.uk/ . Bring this token with you to get online quickly, although you won't be able to connect until you arrive in Cambridge. For most devices that's all you need. Some need more complex setup - see http://www.ucs.cam.ac.uk/wireless/eduroam/localusers for details.
All undergraduate, and most graduate, rooms have wired (Ethernet) network points installed for high-speed Internet access. This is faster than the wifi but requires your computer to have an Ethernet socket. Laptop and desktop computers may have one, Phones and tablets will not. If you would like to use the wired room connection, information and a link to the application form are here.
It is not essential to have your own computer - general computer facilities are provided by the College and elsewhere in the University - but many students find it easier to work in their rooms, the libraries or in other places around the university and Cambridge generally.
Microsoft Office 365 ProPlus is available free through the university. See here for more details.