Appearance -> Menus. The twentyten theme supports one menu, so create a menu and then add the pages, categories, posts etc you want using the boxes provided. You can rename the menu labels etc. To create a sub menu just drag the menu item (once in the menu box on the right) to be in the sub menu under the parent heading and then drag it a little to the right (you'll see a greyish box appear and see it moving as you drag iirc), then drop it.
I've not really used the theme so not sure how the sub menus then display.
Depends where you want to add adsense. I wouldn't just edit the theme as on an upgrade the files will get overwritten, so either create a child theme (
http://www.bloggingtips.com/2009/05/21/wordpress-theme-inheritance/) or use the widgets (Appearance -> Widgets) and add a text widget and drop the code in there. Or install an adsense plugin and it'll probably do everything a lot easier for you. Haven't used any for ages so can't really recommend any.