Users with similar privileges are grouped together. The purpose of a group is to define settings for the group as whole rather than each individual user. Permissions that apply to the group are inherited by its users. You can edit groups in the Security app.
By assigning a role to a group, all users in the group will inherit the permissions granted to the role. You do not have to add the users to the role individually.
You can get a list of all permissions assigned to a user or group with the Permissions app.