Permissions can be assigned to an individual user, group or for all users. These access permissions are set by a Manager (or Administrator) at the folder (or page) level.
Your folder structure, navigation and permissions will need to work together. The folder structure will expand the way the links (navigation) will work. You will likely want to assign permissions on the folder basis, instead of at the page level, whenever possible as it will be easier to manage. It is best to start at the top of your folder tree and grant everyone in your area read access. Then apply write access at the sub folder level. You can assign varying permissions to different sub folders within in your site.
New files and folders always inherit the permissions of their parent folder. However, it is possible to use the "Apply to children" feature when assigning permissions. This will apply permissions to all existing files and subfolders. As this impacts current children (sub folders), special permissions that have been previously set will be removed; you should only use "Apply to Children" if your sub folders do not have permissions that differ from the parent folder.