4
Okay, it's relatively straightforward.
By default, your site's index page is called "top page". The content of your "top page" id set in Admin>blocks. You can add blocks from modules or make your own "custom blocks" (where you make the content).
Alternatively, you can set one of your installed modules to be your home page. Set it in admin>preferences.
If you want to add lots of pages then you'll need a content module as per my earlier post.
The main menu will automatically build as you install modules or you can use a module such as "MultiMenu" to build your own custom menus.