The Twenty Ten theme provides drop downs from Parent pages to child pages. You can create "child pages" which some also call "sub-pages". See the instructions in the support documentation here for creating static pages > http://en.support.wordpress.com/pages/
When you create a static page you can assign it to be either a Parent page which will display a page tab in the horizontal menu (black band), or you can assign it to be a "child page" of any Parent page you choose, and it will display in a dropdown beneath the Parent page you assigned it to.
So create a static page and then look in the right hand column and find "Attributes". Below that you will see the following - click and make your Parent or child Page assignment there.
You can arrange your pages in hierarchies. For example, you could have an “About” page that has “Life Story” and “My Dog” pages under it. There are no limits to how deeply nested you can make pages.