A top-level menu is sometimes also called "global navigation" or a "site menu." Usually seen across the top of a page, it gives users access to the major broad sections of the site even if they go very deep into areas that have specific section menus. Using just a quick snipet of code from the simple common functions you can add a top-level menu to the top of your page template in just a few minutes.
Find your template in the tempaltes folder and open it for editing. Create whatever container you need to hold the menu (usually a DIV with an ID for CSS purposes) and insert the following snippet of code.
<?PHP GenerateMenuToParentUL($CurrentPageID, $CurrentUserID, 1, false, 1, false);?>
This will create a menu that shows all the children of the homepage, but none of their children (since you set the depth to "1"). Save the template and close it. Open your CSS file and add any CSS you need to make the menu look appropriate on your page.
If you're editing an existing template, login to the management console and click on the "templates" tab. Click on "Update All Pages" on the line for the template you just updated.