Permissions are the roles that are assigned to users, modules, and pages so that a user can either view or edit that module or page.
If a page has a role added to permissions but the user does not have that permission tied to their account, they cannot edit the page.
There are 3 selections in the permissions area. They act as a check box and can be one of 3 things...

-First sign - The check mark enables that ability
-Second sign - The disable sign should NEVER BE USED
-Third sign - Use this when you want that group to not have access to view or edit.
The default permission template looks like this -

NEVER allow all users to edit!
Never use 
