Usually, modules in PrestaShop must be configured before the usage. Module to generate voucher code for next purchase also requires configuration before it will start to generate voucher codes for your customers. Below you can find informations about sections where you can configure the addon. Rewards addon from mypresta.eu is easy to configure and it is not necessary to prepare any kind of advanced settings.
More details about module's configuration you can find on next chapter of this documentation "Configuration" (See left hand side menu).