This is for the new iPad Pro 2018 running iOS 12, this device doesn't have the home button anymore.

There are multiple functions activated by swiping up from the bottom of the screen, depending on how quickly you do it and how far up you swipe.

Let's say you're in an app. Slowly swipe your finger up from the bottom of the screen (keep the finger pressed down) and you will see the app dock rising up. Let go and the dock will sit on top of the current app, and you'll be able to open a different app, potentially in split screen mode.

Swipe down on the dock and it will disappear again - unless you're on the Home screen, where it always shows.