Closing apps? On iPad Air 4th generation

See the following from Quit and reopen an app on iPad - Apple Support

Quit and reopen an app on iPad

If an app isn’t responding, you can quit it and then reopen it to try and resolve the issue. (Typically, there’s no reason to quit an app; quitting it doesn’t save battery power, for example.)

1. To quit an app, open the App Switcher, then swipe up on the app.
2. To reopen the app, go to the Home Screen (or the App Library), then tap the app.

Swipe up from the bottom edge of the screen and pause in the center of the screen.

Or for a device with a home button, double-click the home button.

Also note that when you see text in blue, you can click on that for further information. See the following from my previous reply:

1. To quit an app, open the App Switcher, then swipe up on the app.

Sorry did not notice the previous response