Usually each module in PrestaShop must be configured before the usage. The same is with gift cards plugin. This is why module has inbuilt configuration page where you can manage settings of the module. This "configuration" page is available in shop back office under "modules > modules" section
Module configuration page
This page has 4 sections: Main settings, Define vouchers, Guide, Updates. First two sections are related to settings of the module, last two sections contains some informations about the module + possibility to check availabiltiy of plugin updates.
History of generated gift cards
Right after installation module creates also section where you - as a shop owner - can explore the list of gift cards that customers generated. It is available under "price rules > gift cards" section. You can see there information about all gift cards that module generated for your customers that will help you to identify the order, customer and voucher code.