how do turn the orientation to display the sideways (horizontal) instead on up and down (vertical)?

[AC Question]

self explanatory...

 

[hallux]

You may think it is.

What device? What os? What launcher? Under what circumstances are you looking for the screen orientation to change?

In the quick settings on recent versions of Android is a toggle for orientation. Make sure that's on. The Google launcher recently added screen rotation on the home screen.