If you are referring to Google Chat see the following link for information as Google ended support for it.
Google Chat on EM Client - eM Client
Otherwise “if you are both” using a compatible XMPP / Jabber server-host, you can use that to chat.
(To setup a XMPP / Jabber network chat) go to “Menu / Accounts” and click “Add Account / Chat”)
You then put in either your exiting registered Jabber usernames & passwords, or register a new acct.
