Difference between Navigation and Page Access

I cannot understand what the difference between the Admin>Builders>Navi Menu and Page Access Control. Do they do the same thing? If not how are they different?

My understanding is that we use Admin>Builders>Navi Menu to control the visibility for the menu tabs for Guests and Members... and we use Page Access Control to control access to a page.  For example, I have hidden the menu tabs for all Sound related pages but if I type in the URL for the Sound home page [/m/sounds/] it will display all information.  That's not what I want, so next I use Page Access Control to deny access to all pages in the Sound html folder [/m/sounds/*] .  Now if I try to view the "sound" home page I will see the message "You don't have permissions to access this page". Note: site admins will still be able to view the page.

 Ok, so one is visual (Navi) but could be accessed with right URL and the other (Page Access) is total no access.

Thanks