Creating and Managing User Groups in SharePoint
Site owners in SharePoint can create user groups in order to organize site members and manage access. After creating a group, you can limit folders and file permissions based on groups.
It is not necessary to create a user group to add members to a SharePoint site. To simply add members to a SharePoint site see Add others to a SharePoint Site .
Follow these guides if you have first reviewed Restrict SharePoint folders from certain Users and you have more than one group of users that you would like to hide folders from.
User Groups are required for folders that contain more than 100,000 items if you need to restrict access to the folder.