It depends on how much control you want that person to have in your ring. The only way to share a ring is to give them your user name & password for the ring. If you want them to have all the responsibility of adding new members - then you would also have to have a different email - maybe set up a generic one you both could use and have access to just for the ring. Then both of you can add people and do ring business as needed. Remember - giving out your ring access could cause problems in the long run - depending on how much you trust the other person - they could just take the ring, change the user information - and you've lost your ring! If you have other rings - consider changing your login in and password for this ring so the other person has access only to the one ring. Just some added food for thought.
