Board Thread:Support Requests - Getting Started/@comment-26370267-20150504211408/@comment--20150505021632

If you mean, how do you join the chat room on a Wiki, simply look towards the right side of your screen, and where it says "Join the Chat", click it! Then depending on your browser, a new window will pop up and you'll be in the chat room.

Alternatively, you can go to Special:Chat to join.

Lastly, if you mean how do you activate chat you are an admin on, you can enable it at Special:WikiFeatures :)