Your User Role allows you to "open" the drawer that corresponds to that role. If you have EXECUTE permission, you can create objects for that drawer. For example, if you are a Dashboard Designer, you can create dashboards on the Available Dashboards page.
When you create an object, you are the owner of that object. You have WRITE permission for the object, and you can set the permissions for that object for users in your Group only.
If the user's group belongs to the All Users Group, the option to set permissions for non-administrative users is disabled. Hence, only the administrative users can set permissions for the All Users group.
If the object is still a work-in-progress and you do not want anyone to access it yet, you can make it "private" by leaving all permissions unchecked for both the All Users and the Groups.
When the object is ready, set your default Group (My Group) permissions to EXECUTE or even WRITE. For example, if you create a Dashboard for your Group and the dashboard has notes, you might want others in your Group to update the notes.
Even though you are a Dashboard Designer, if the Available Dashboards page contains dashboards created by (owned by) other Dashboard Designers, you may not be able to see those dashboards, based on your Group permissions and on the object-level permissions those owners have set for their dashboards.