windows sliding

It is a bit unclear what you are saying, but I am guessing that you have more than one "Space" (also known as "Desktop".

If you want, you can close all but one Desktop and that will put all your windows, for all applications, there.

Go to Mission Control (you can click the appropriate key or swipe up with three or four fingers on the trackpad, or start Mission Control in several other ways - from the Finder, Launchpad, Spotlight... like any other application).

Then go to the top area and click the X to close desktops. The X is not visible in my screenshot below, but will appear in the area marked green when you move your cursor there.

Hello peggy3807,

Thanks for posting in the Apple Support Communities.

Based on your post, Split View may help in what you're looking to do with your apps on your MacBook Air. Check out the steps below for assistance with using Split View, and the following resource includes more details about this feature: Use two Mac apps side by side in Split View - Apple Support

Enter Split View

Follow the appropriate steps, depending on which version of macOS you're using.

macOS Catalina or later

1. Hold your pointer over the full-screen button  in the upper-left corner of a window. Or click and hold the button.

2. Choose ”Tile Window to Left of Screen” or ”Tile Window to Right of Screen” from the menu. The window then fills that side of the screen.

3. Then click a window on the other side of the screen to begin using both windows side by side.

We hope that's able to help. If not, provide more detail for us to gain a better understanding of what's happening.

Have a great day!

It does not seem that we are speaking the same language. By Mission Control I did not mean its preferences, but the actual Mission Control - see my screenshot in the previous post.

You can reach Mission Control in several different ways: the easiest is to swipe up on the trackpad with three fingers (or four fingers, it depends on your settings).

The question is: how many things do you see in the top row, like the image below?

Note that if you put applications in Full Screen, each of them will get its own separate desktop.

For example, here is one where Safari was in Full Screen:

Luis -- When I go to the Mission Control page, I don't see any desktop selection option. I see a list of circles to check, none of which seem relevant, but I must admit that I don't understand what any of them mean because they refer to "Spaces", and I don't know what that means. I tested a few of them, and they did not do anything to stop the application sliding off the screen when I move it close to the edge to better see a second application on the screen. How do I prevent one app from sliding off the screen when I push it to the side to see another.

Thank you. I closed the second desktop on Mission Control and hope that will do it.