You will be able to see most of the information pages on Civvy Street without logging in. However, there are a number of services which are reserved for registered and approved Civvy Street members.
If you register (and are approved) you will get access to more of the site and additional services to assist you. If you are a member of the Services or ex-Services community you will need your Service number. Once this has been validated, you will be given full access to all of the member areas of the site.