First you have to enable tablet mode. This activates the 8.1 style "swipe down from top" action for closing apps. Open an ap, and swipe down, but instead of dragging it to the bottom, drag it to the left or right edge. You will now be in split screen.
It will immediately open up a task view in the empty half of the screen allowing you to select a running app or window to populate the second half of the screen, and you resize with the centre slider like on 8.1
I've not personally found a way of having 3 windows/apps open in tablet mode, nor a means of using the quadrants. Maybe that is reserved for desktop mode.