App icon disappeared

[MagicBob]

I installed an app on my new Pixel 3XL (my first smart phone). At first the app didn't show up on the display, then the next day it did. The next day it was gone again.
1. How can I get the icon back to stay?
2. How do I access an app when the icon is not on the screen?

Bob

 

[Rukbat]

Go into the app drawer. Find the app. Long-press it and drag it to the desktop.