Your question about making a second and third page has two possible answers, depending upon whether
1. you are referring to pages that appear as tabs at the top of your blog, or
2. you are referring pages that are "children" of the tabbed pages.
In case 1, you just create a page whose parent is "Main Page" (see tabs to the right of the edit space).
In case 2, if your theme recognizes "children" of the "children" of the Main Page, (again, using the "Parent" tab to the right) you will set the new page as a child of the page you wish it to link from, and in that way create a heirarchy. Even if the theme does not recoognize it (and some don't) it will still be there, but only accessible through the Manage Pages route.
I sounds more complicated than it is.