Use the search box at the top of the page to search by a person's name or email address. To the right of their name you will see a link to Add friend. Easy as pie! Once they confirm you are indeed friends, you will be able to view their registry and find them on your My friends page.
They can also send you a link to their registry, and in that case there is also an Add friend link to the right of their profile picture.
That means that you sent them a friend request and they haven't responded to it yet (accepted or declined).
From the Share page you can send an email to friends and family encouraging (or nudging) them to create their very own giftbug registry. You need a place to go to find them the perfect gift too!