Question: how to use multi window on galaxy tab a?
Answer: Open the apps you wish to use as you normally would. ... 
Tap the “Recents” ... 
Tap the multi-window icon located to the left of the X in the app window. ... 
Tap the multi-window icon (looks like an = sign) located at the upper-right corner of the app.
Select another app to run both apps in split screen multi-window mode.