To communicate with your opponent, select the chat option.
It can be found in the game and it is represented by the three-dots icon, on the upper right corner of the screen. Once you do so, a new window will be opened and you'll be able to contact your opponent.
To start chatting, simply type in a message. Remember, be nice to the rest of the users!
On the other hand, on the upper right corner, you'll see the three-dots icon again. If you tap on it, you'll be able to start following your opponent.