How do I open and configure Twitch Chat?

Open the XSplit Gamecaster Overlay by pressing [Ctrl] + [Tab] (or the hotkey you assigned to it) and hover over the Twitch logo and click on the chat icon:

This will open the Twitch Chat window where you can send and receive messages:

You can also set the Twitch chat to be visible in your stream/recording and in your in-game HUD:

Change the text color for your viewers’ messages, your own messages, and adjust the opacity of the Twitch chat window:

Adjust the text size:

And, finally, show/hide the list of your viewers: