There are 2 ways to invoice the guest after raising an invoice:

Printing it During Checkout

You can either 'Open' or 'Save' the pdf. The pdf file can be printed:

If you don't have it already, and your computer is unable to open the file, download a PDF reader.

E-mailing it to the Guest

The e-mail will be loaded in automatically from the Contact. It can also be edited to a different e-mail address if required:

Click on [SEND] to send it to the guest, or [DON'T SEND] to return to the previous window.

More information on how to Invoice an Agent.