Press on the App switcher icon on your smartphone screen. Multi tasking window would open, now tap and hold any of the app on which you want to work and drag it to the top of the phone screen. This app will automatically occupy top half screen of your smartphone and remaining half screen would still show app switching screen.
Now you have to choose the second app for working on bottom half screen of smartphone. Apply the same above Drag and Drop method for this and select app for bottom screen.
Congratulations…now you have two apps on the same screen of your smartphone to work on both of them.