As soon as you arrive in Berlin you should arrange a meeting with the project managers of the PCD network.
Professors and PostDocs will then receive a confirmation of their status as a visiting scholar at Freie Universitaet Berlin. You need this document in order to apply for a library card and Internet access. Additionally, should you wish to open a bank account without a certificate of registration, you will receive a confirmation of your address.
M.A. and PhD students will also receive a confirmation of their address, and the rest of the registration procedure will then be explained to you.