$Membership allows to access users and organization database objects.

You can use $Membership.Administrator property to access domain administrators group.

If you need to query specific identity you can use $Membership.FindIdentity or $Membership.FindPosition to find by certain criteria or you can directly query the identity with $Membership.Get method.

If you have an identity and query it's properties you can use the $Membership.GetProperty to get certain properties.

If need to find manager of a user or position or organization unit you can use the $Membership.FindManager to perform complex query.