Add more users to an external system

QI can start my old 2011 iMac up from an external SSD, letting it run faster, but how do I go about installing another user on that system?

AWhen you install macOS on any disk, it creates the first admin user, and you shouldn’t alter that. Obviously, once that has been created, you can always add more through the System Preferences >

Users & Groups pane. Open that, click the padlock icon and authenticate as that admin user. Then click on the ‘+’ tool at the bottom of the list at the left to add a new user.

You then get to choose whether they’re set up as another admin or an ordinary user, and other details of that account. Once you’ve created an additional user, if you log on as that user you can run Migration Assistant to migrate their files from another system or backup.

The first and most important choice is whether to give a new user admin rights, or a standard account. Give the new user a basic but secure password, and let them change that to one they can remember reliably.