This method is to activate the emergent notifications and to read the messages (in case they are not very extensive, since it only picks up a limited amount of characters) on the desktop of the smartphone when they are sent to you. In iOS, this is done through «Settings» and, in Android, accessing WhatsApp -> Application settings -> Pop-up notifications -> and «Always show pop-up».
For Android, you must activate the Wasap Widget, access the option “Enable Widgets” in “Settings”, click on the one of the app and drag it to the screen.
You can also press an empty space on your phone screen for a few seconds and in the Widgets section drag the Wasap Widget and Widget 4×2, you can read the received messages without having to enter the app. Enlarge the Widget if you wish or create a new screen and put it there.