How Prosites synchronized with WHMCS?


I use the following plugins:
- Prosites
- WHMCS Provisioning
- WHMCS WP Integration


I mainly use ProSites to create my client sites but there was not managing invoices, so I installed whmcs.

How work whmcs provisioning with ProSites?

My customers can order directly from ProSites? Orders are then synchronized with WHMCS? or else he will be directed to the customer whmcs to place an order?

what is the ideal integration be more simple?

Thank you in advance for your answers to these questions