Forest Admin's user permissions can be summarised by the following features:
Teams: You can have as many teams as necessary. Each user can belong to 1 or more team(s). Each user has 1 role which applies to all the teams he belongs to.
Team layout: The layout of a team is the way every visible aspect of your UI is set, from columns to smart views to widgets.
Roles: Roles allow you to manage all Smart Actions permissions, Collection permissions and access to Environments applied to a group of users. Each user has 1 role which applies to all the teams he belongs to.
Permission levels: The permission level of a user determines what Forest Admin administration permissions he has (e.g. Admin, Developer, Editor, User).
Scopes: a scope is a pre-defined filter which applies to a collection and all its segments. It can be applied to specific teams.