In order to join in the chat for bingo you simply need to go to the game as you usually would, then at the bottom of the screen you will see 4 buttons:

Ticket view

Game view

Chat

Mini games

The first button will show you how many tickets you have purchased for the game, and will also allow you to buy tickets, and bulk buy them for upcoming games.

Second is the game view, this is where you can see the balls being called and track your progress.

Third is the Chat room, here you can chat with the hosts and other members as normal, it will also show you a cut down version of the Bingo game, so you don't miss seeing anything. The smaller version still has the normal functionality, if you click the blue arrow in the bottom right corner you can alter the room you are in, see a list of people in there and alter your text size and colour.

Lastly is the mini games section, you can play Slots whilst you wait for the next Bingo game to start, you will still see the balls being called as well on this screen.