Getting the Messenger Customer Chat widget live is as easy as clicking the "install" button but you'll probably want to customize it a bit.
Here's how it works
When you click on the "customize" link from the installation card, you'll be presented with the plugin editor:
Using the editor you can create an automated reply when someone sends you a new message. A new message is sent only when there is not an existing conversation between you and your customer.
The two greetings are displayed (not sent) on the dialog (see below) depending on if the user is signed into their Facebook account or not when they visit your site.
The greeting dialog display option allows you to control how the dialog is shown when a user arrives on your site. The default is also "shown".
Lastly, the icon is blue by default but you can stylize to match your site's theme. Do so by using the color picker:
NOTE you may need to refresh your store's page to see the change.