You need a Starter plan or higher to have granular teams and roles permissions. Without granular permissions, all users will have the same default permissions.
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.