When the main portal settings are adjusted, you can start adding users. The most simple way to do that is to click the Invite users to portal button at the left side panel in any portal module. Please refer to this article to learn more on how to add users in different ways.
Using Control Panel, you can also import the necessary users and groups from an LDAP Server.
After you add users, you can go to Settings->Security->Access Rights and restrict access to some portal modules making a particular module accessible to the selected users or groups only.
To learn more about the capabilities of your portal modules, please refer to corresponding sections of our Help Center: Documents, Projects, CRM, People, Community, Calendar, Mail, Talk.