Click on All Communities to list all available communities.
Click the Actions button for the selected Community, and select Assign Members from the menu.
All the current members of the Community are listed.
Click Available tab to list all available users.
Select the checkbox against each of the users who you want to assign as members. For example, select the checkbox against the user Joe Smith.
Click Update Associations button to assign selected Users as members.
Click on Current tab to view the users who are current members of the community.