Adding users to groups is a convenient way to grant access to the different collections. Indeed, rather than multiplying the number of user access to a collection, you can add users to a group and grant a group access to a collection. 

Adding users to a group

1. Go to the Users & Groups module
2. Select the Groups tab
3. Select a group
4. Once in a specific group, select the Members tab
5. A list of users already members of this group is displayed
6. Select + Add members
7. Select one or more users and confirm

Image : Adding users to a group