To set yourself as available to chat and allow your website viewers to contact you simply click the status button in the top right of the admin panel
When you are offline you will see this red button. From the customers perspective they see a contact form. Clicking it will set you to be online.
When you are online the status button will turn green and you will see a wave animation. This will switch off the contact form and allow your website viewers to chat to you. Clicking the status button will set you to be offline:
Each User sets their Online/Offine status seperately. If any User is online then the chat will become active. If no User is online then the chat will be replaced by a contact form.