Your site is made up of Admin pages and Content pages. 

Admin pages are built into the system and cannot be added or removed. Admin pages are used by Administrators and content authors to setup users, create/edit site content, and to upload document and image files. 

Content pages contain the the text, images, links, etc. that makeup the content of your site. Content pages may be setup so that all users or only logged on users may access them.

The Content pages in your site or organized in a heirarchial fashion. Usually you will have several top-level pages with muliple sub-level pages beneath. The sub-level pages may have sub-level pages as well. This parent-child organization is used to dynamically build your sites main menu.

By default, Content pages are included in your sites main menu. Alternatively you may exclude any page from the menu (hide), create a placholder to sub-level pages (disable), or set the page up as a link to a file or URL on another site.