Book Guard does not automatically send the code to the customer when they order your product. This is something that you will need to setup with your web host - it is a very straightforward process. You just setup a simple database that works alongside your ordering system. The database can be designed so that when an order is placed and approved, a code is sent to the customer and their information is entered into the database alongside the appropriate code.
This is a very simple procedure that just about any web programmer who is familiar with ordering systems could do quite quickly. In fact, if you are using proprietary shopping cart software with your ordering system, this may already be a built-in feature!
You may also e-mail the username and password by hand.