Get started with Chat in Google+
The Google+ chat list will be automatically populated with people you’ve already chosen to chat with in Gmail. If someone isn't already a contact of yours, you can invite them to chat right from the Chat search box.
Note: We're aware of an issue that prevents Chat windows in other Google properties from syncing properly with Chat windows in Google+. We're working hard to fix this problem. If you're using more than two Google properties simultaneously (for instance, Gmail and Google+) we recommend temporarily signing out of Chat in the other property and using Chat in Google+.