How do I use URL aliases in menus? I am kicking the tires on Drupal 7 by spinning up a test site. 

I chose the Danland theme and created various pages with URL Aliases for each, but when I create the Menu link for each, I can only enter the node in the "Path" field for the menu link and not the alias. So I can only enter "node/20" and not "about-us" (the alias for the node) in the menu.

I'd like the menu items to resolve to the aliases and not the nodes.
How do I do that?
Like Berdir mentioned in the comments and Greg mentioned in his answer, the following methods of adding path aliases should Just Work™: 


Adding it on the node submission form during node creation/editing
Using Pathauto to automatically create aliases for nodes.
Adding aliases manually by going to Configuration &rarr; Search and metadata &rarr; URL aliases


That it's not doing that is weird. Try clearing your cache by going to Configuration &rarr; Development &rarr; Performance. This should rebuild Drupal's menus and get the path aliases to show correctly.