Hi,
Ok, well, people can join groups if you have made it public and joinable, but you can also add them from the list by clicking on "Add New Member". When you view your group from the My Groups list (which shows the groups you have created AND all the ones you are a member of) you will see this button on the bottom, under the list of group members.
Click on this and then you can search the PokerDIY member list. Ultimately I want to have a way of inviting non-registered users too, but for now you can just use the
Tell a Friend form to tell them about PokerDIY ;)