You add your address to your account, and it takes a few seconds to do. It just verifies that it is an actual physical address. You need to go to my listia and then the link to edit your account is on the left hand side about halfway down the page i think
I'm sorry, its called "youre saved addresses" under account settings on the left hand side of the page once you go to the "my listia" page :] hope that helps!