To quickly swap between open apps on your Mac, hold down Cmd (keep holding it down) and then press Tab to cycle through your open apps from left to right.
When you get to the app you want to access right now, let go of Cmd.
Bonus tip:
If you want to quickly close an app while you are in app swapping mode, keep holding down Cmd, go to the app you want to quit (by pressing Tab) and press the Q key on your keyboard.
Here’s a quick video of me first opening an app, then swapping and closing two open apps by hitting Q:
