We enabled chat on our Community. For you to be able to use chat, you'll first need to add other Community users to your list of friends within the platform. An easy way to do so is to hover over the user name, click "add as a friend" which will then open a little pop-up window where you can add a few words. Once your friend has accepted your request you'll then be able to chat with him/her.
You can also chat with multiple users within the same chat. You only need to drag/drop users you'd like to add to the current discussion.