It is easier said than done I guess. We devote many man hours to documentation and tutorials. The reality is that to really understand everything you need to know the underlying technologies including Dreamweaver, SQL, HTML, CSS, and PHP. Even though we put them all together in a relatively simple interface, our documentation would have a difficult time truly explaining what happens under the hood.
Anyway to add admin and users to your table you could just add a single column: isAdmin.... set it to a tinyint and use a checkbox in the admin to set the value to "1" for admin and "0" for non-admin users.
Default it to "0" and anyone that registers will be automatically non-admin.
Then update the User login page Server Behaviors that authenticate the user and store the value of the IsAdmin column into a session variable during the login process (by default just the userID is stored).
Then open up the rules interface from the Modify menu and create a new Rule: "Is Admin" and set it to
Allow if: <?php echo $_SESSION['IsAdmin ']; ?>
Then you can use that rule to restrict access based on the column value you created to identify admins.
You don't have to follow this exactly... column names, values, and rule names can all be whatever you want... the keys are:
1) Create a way to identify Admins in the users table you are using to login
2) Store that column you are using to identify Admins as a session variable in the login process
3) Create a rule based on that Session variable to allow you to restrict access based on it