Samsung Galaxy Note 4 - Manual (Page 61)

Motions & usability features
61
Adjusting the window size
Drag the circle between the app windows up or down to adjust the size of the windows.
If Multi window is not activated, open the All apps screen, tap Settings → Multi
window, and then tap the Multi window switch to activate it. Alternatively, open the
quick settings panel and tap Multi window to activate it.
Pop-up Multi window
1
On the All apps screen, launch an app to use in a pop-up window.
2
Drag down diagonally from either end of the top edge.
The app screen will appear in a pop-up window.
Switch to a floating icon.
Close the window.
Switch to the full screen
view.
Move content.