As a postdoc at UC Berkeley you are entitled to a number of privileges. To use your privileges and access many of the resources which are available only to the UC Berkeley community, you need to obtain a CalNet ID.
How to get it? Once you arrive, ask the administrator in your Department to provide you with a temporary "token" (numerical code), which is used for activation of your CalNet ID. Click here to activate your CalNet ID and follow the instructions.
At first, your CalNet ID will be by default the same as your employee ID. You should change your default CalNet ID to a self-selected value (once only!) using this link. Things to consider when choosing your permanent CalNet ID are described in detail here.
CalNet ID is necessary to set up your E-mail acount, which can be set up here.
Also, with your CalNet ID and a valid government document (such as your passport or your country's driver's license) you are eligible for the Cal 1 Card. Also, be prepared to have your photo taken! The Cal 1 Card is your official University ID and it has a number of functions from access to the library to your debit card, if so desired. Check out all the functions here.