Samsung included a cool feature from the Note 4 called Pop-up View that works with any app that supports Multi Window (and only those apps).
Basically, you get a realizable floating app window that you can move around the screen. You can even have more than one and minimize them to floating icons.
There are three ways to go about this: long press on an app in the multitasking UI, drag down from the top right corner when an app is open, or use the pop up button when you have an app in Multi Window mode.
You can arrange these floating windows however you want, drag content between them, and maximize them to full screen at any time.