This feature is the integration of Zendesk Chat's live chat solution into a store, to enable its visitors to request a real time chat with its customer support team (when available). It aims to build consumer confidence in a store and its service, with the ultimate aim of increasing sales.
Please note that you're required to have an active account with Zendesk Chat to enable this feature, and are responsible for any licence/registration/ongoing fees associated with the service provided by the third party. Also, there are limitations to the visual appearance of the 'Chat Now' button created for this feature, due to Zendesk Chat template limitations.
This functionality is not compatible with standalone mobile sites.