First, decide how you want your pages protected: either on a one-to-one user-to-page relation, or on a many-to-many user-group to multipe pages.
If you plan on granting access to individual pages, to specific individual users (Bob Smith gets access to bob_smith_details.htm, and Mary Rogers gets access to mary_rogers.htm) then you could skip along to restricting pages.
However, if you plan on granting access to a group of pages to users of a particular user group (a_team_roster.htm, a_team_practice_schedule.htm for all users of the user type "Team A", and "b_team_roster.htm", "b_team_playoffschedule.htm" for all users of the user type "Team B"), then you'll first need to create those "User Groups"
Then, once you're ready to restrict pages, and you have your pages published up to your website, log in the administrative area and to restrict the access on those pages.
Allow clients to view information for their eyes only.
Grant access to members of a sports team to get practice and roster information.
Prevent non-authorized users from viewing sensitive information, such as preferred price lists.