Use the Super key
When you press the Super key, you will be able to see your desktop. You can also press Super + S to see all of your open windows at the same time. This key can usually be found on the bottom-left of your keyboard, next to the Alt key, and usually has a Windows logo on it. It is sometimes called the Windows key or system key.
If you have an Apple keyboard, you will have a ⌘ (Command) key instead of the Windows key, while Google's keyboards have a magnifying glass instead.
To change which keys are used to display your open windows overview:
Type "Settings" into the global search bar on your desktop. Click on the resulting Settings icon, or press Enter, to open.
Click the Shortcuts tab.
Select System on the left side of the window, and Show the activities overview on the right.
Hold down the desired key combination.