In this example, we will add a new user to the "Downloaders" group

Here we can view the permissions that have been assigned to this group

Click the "Role picker" field and start typing the email address of the user to be added. 
Select the user when the search completes and click "Add"

Click the "Role picker" field and enter the user email to add 

The user has now been added to the group, and will inherit the permissions assigned to the group, and access any records, media or collections to which the group have access. 

Add an existing user to a group