Board Thread:Friend Code Exchange/@comment-178.85.120.213-20180113144723/@comment-2601:486:100:4AB0:4DCF:5BB9:C0D8:C1E8-20180113153759

Go to Add By Code on your Friends tab. On the left you will get a current code to invite friends and on the right is where you enter codes posted by those seeking friends.

More info here: http://the-secret-society.wikia.com/wiki/Adding_Friends?action=edit&section=2