Enable Text To Speech
First open the Android Settings app and go to the 'Language and Input'. In the example below, in the tablet I used, it was under 'Additional Settings'. This may differ in your tablet, but the 'Language and Input' configuration will be present.
Choose the Text to Speech and option and enable it. It is recommended to use Google Text to Speech Engine for the tablet. This is available from the google play store. (Some problems were observed with the Mi pad default engine)
Enable Playtalk Keyboard
In the 'Language and Input' section, you will see the 'Playtalk AAC Keyboard'. If you have already installed the older 'Playtalk Keyboard', that will also be visible (it is recommended to uninstall the older keyboard). There are three steps involved.
Step 1: Enable the Playtalk AAC Keyboard
Step 2: (May be optional depending on your tablet). Set the default keyboard (the option above Gboard that you see in the above picture). As you can see, it will show the current default keyboard.
Step 3: (May be optional depending on your tablet). Set 'Playtalk AAC Keyboard' as the default keyboard.