User Groups are used to manage Site membership. When you assign a User Group to a Site, the group’s Users become members of that Site. This is one of the main use cases for User Groups.
Follow these steps to assign a user group to a Site:
Open the Menu (), select the Site you want to work in, then open its Site Administration menu.
In the Site Administration menu, select People → Memberships. This opens the Site Memberships screen.
In Memberships, select the User Groups tab. This tab displays any User Groups currently assigned to the Site.
Click the Add button (), select any User Groups you want to assign to the Site, then click Done. The user groups you selected now appear in the User Groups tab.