Was introduced already back in 2014 with Android 5 ( lollipop ), and something I personal not used. Most people have their own phones anyway so I would guess it's not a very common used feature. Available in Settings/User and Accounts. Tested and it was super easy to setup and enable, but it's obvious it still have a few parts that one should know about. One example reported is that full access to SD cards is still possible. Was though not possible to change the settings for installing apps from external sources, as that was locked by the admin account. No share of Google accounts and if wanted, it's possible to disallow phone calls and sms. But I have no idea if emergency calls still works.
www.howtogeek.com
My own phone also has something called Maintenance mode that is advised to enable before handing over the phone for support. I would guess guest mode is pretty similar.
How to Set Up Multiple User Profiles on Android
Make profiles for multiple people on your Android device.
www.howtogeek.com
