If you do not have a webshop connection that supports automatically created discount codes, you can simply upload codes for your ambassadors to fetch instead.
To upload these go to Settings > Sales & Discounts and choose the 'Manually upload discount codes from webshop'
First you need to create the discount codes in your webshop and upload them using the template.
You will be notified once you will need to upload more codes, i.e. if your codes run out or close to their expiration date
Check out this video showing how to upload your codes and how it will show for the ambassador: