how do i use splite window in my lumia 730 windows phone build 1511

i Just update my phone from 8.1 to 10 build version 1511, and i found a new feature that is one handed use or split window. But i dont know how to activate it? Because when i tap and hold win logo on task bar, its split my window but i can not place anything on the splited aria. so i need a help from here.

Surjava Basak
India

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