How do I create gift vouchers that my customers can buy?

Gift vouchers are treated as normal products, and created the exact same way. This feature is however not present from version 3.2 and on.
The only difference there is the demands for the "Model" field at the bottom of the create new product page.

The Model field
The system sees a product as a gift voucher when the "Model" field begins with "GIFT".
What comes after the word GIFT does not make any difference to the system, therefor there is nothing wrong in creating multiple gift vouchers of different values and using different "Model" definitions. As an example one could imagine using "GIFT10" for a 10 USD gift voucher, and "GIFT20" for 20 USD voucher.

What happens in the shop when a customer buys a gift voucher?
When a customer buys a gift voucher it will appear in the voucher queue in the administration. Here it will stay untill the admin approves the voucher (typically done after payment has been registered).
When the voucher is approved an email is send to the customer with a code. This should then be used when the customer places an order.