This is how to use multi-window feature in an Android Nougat 7.0 Device:
I) While in an app, hold down on the Recent Apps button.
II) Select an app from your recent apps. If the app you want doesn’t appear in that view, tap the Home button. Not all apps support multi- window mode. You will see a warning if it would work for apps you select.
III) Proceed to tap a second app. You have set up split-view. Then drag the dividing line left and right to resize, tap Home to find a new secondary app from the home screen and tap the Split Screen button in the bottom right corner to select a recently used app.