[help, how can Separate the interface of my users]

Php programmers out there, pls help me my programming problem. <br>
I have three page : <br>
          [b]first page[/b] : for the administrator side where The administrator able to create a user
                        the sample input are 
                                <li>User name
                                <li>password
                                <li>user type
          <br>[b]second page[/b] : A client page where the  user (client) can view the unrestricted area      or            information of the company. <br>
          <br> [b]Third  page[/b] : And login page where the users logins.
<br>
What should I do (what script shall I put) to identity the login name of the users, for then when the administrator log-in he/she can view the Admin page, and if the client log-in she/he can view the client side. Pls help. Thank you.