With the Users module, you can manage the user accounts and their access rights to the portal. The allowed user actions can be controlled by adding or removing roles to/from a user.
To assign user rights in a more controlled manner, you can make use of user groups. By assigning a user group to a user, the rights defined in the user group will be combined with the rights that are directly assigned to the user. When more than one user group is assigned to a user, the rights from all assigned user groups will be combined.
Currently it is not possible to assign installation specific user rights. All rights assigned to a user will be applied for all installations a user has access to.