Larry,
There is one particular page that will be helpful here. When logged in as an administrator or host to your site select "Pages" from the Admin menu.
Here, you can create new pages and modify existing pages. You can also modify the structure of the pages. The menu -> submenu navigation is based directly on the hierarchy that is displayed in the Admin Pages page. If you have a page called Products and two other pages, one called Big Products and another called Small Products, you would want them to appear in the hierarchy this way:
Products
...Big Products
...Small Products
The pages would then show up as sub pages of your Products page.
The other administrative page that will be helpful to you is the settings for individual pages. You can either navigate as noraml to a given site (when logged in as admin or host) and select the "Settings" option from the top left administrative navigation, or you can select a page on the "Admin - Pages" page and click on the pencil icon to edit it.
Also, in the settings page there is a check box in the "Page Details" section that allows you to toggle whether or not the page should be shown in the menu ("Include in Menu?").
Take care,
Ian