Using security roles you can control which users are allowed to access the areas you create and whether they can view, edit and create content in that area.
When you access manage areas you can click the permissions link to assign and remove various security roles for the area.
Members of an area can, by default, view and publish content to the area unless removed using security roles. Users are automatically assigned as members of the area that is specified as their department or office in their user profile.
Each area that exists has a members option (except folders), where users can be added or removed, which can be accessed when managing an area.