Wallpaper Change ~ iPad

I'm not comprehending the Wallpaper change on the lock screen and I can't be spending hours trying to figure it out .

Both pics are in my lock screen . . . I can't get one of them to show up on my Home Screen .

If I try it from the Photos app , it no longer asks which screen do you want it on .

It seems like it would be a simple task . . . I have five years of higher education & 17 years of using Apple products & I'm embarrassed to say that I don't get it .

🤷‍♀️