What is the difference between adding users via the settings menu and adding users via the share menu?

Is Multi-User Administration where you choose the settings for all users, even the ones you invite via the "share" button. Or this only for admin usage.?

These are kind of confusing, especially since I'm trying to set up pogoplug for different users, with different permissions, but still be able to have admin access for 1 or 2. 

Thanks for the help!