Each user logs onto the operating system from the initial screen that displays all users that are currently registered on the device, as well as the options to either Sign On as a 'Guest' user or to "Add a New User".
Where two or more users are registered on a device either can "Sign on" as the only active user and "Sign out" when finished.
If a logged in user does not "Sign out" but takes the option to "Sign in another user [by opening the pop up panel, by clicking on the time in bottom right corner, then clicking on their user icon] then a list of all users registered on the device will be displayed.
You can now select another user and "Sign on" concurrently with their password.
It is then possible to switch between these active users using the pop up panel and clicking on the icon of the currently active user from where other active users can be selected.
For an even quicker shortcut you can switch active users using the "Ctrl "+ "Alt" keys plus either "<" or ">" without having to enter their passwords.