Mapped accounts allow you to map two accounts in order to switch from one account to another very easily and in one step, without having to log out and log in again.
In order to control which user types will have the permission to use this feature, go to the 'System Settings' -> 'Users' tab (1), then move to the 'Advanced' tab (2) and select the option you want from the drop-down menu (3).
In order to add an account to your primary one, go to your personal info (1), then to your Account (2), move to the 'Mapped accounts' tab (3) and click to add a new account (4).
You can then see your mapped accounts and select one for switching in the header of the page by clicking on your username (5). Just click on the account to which you want to switch.