https://www.cnbc.com/2018/06/22/how-to-get-ios-12-public-preview.html

Apple just launched the public preview of iOS 12. That means you can now try the new software features that are coming to iPhones and iPads this fall.

The public preview is a way for Apple customers to try new software that's relatively stable but which might still have bugs and other issues. That means you can try features such as the new Measure application, Memoji, Screen Time and more, all before the final versions are released to the public in the fall.