What is an affiliate program? Affiliate marketing is a promotional model that connects merchants with independent marketers who are willing to invest time and money to sell a merchant’s products.
Why should I use affiliate marketing? Affiliate marketing is performance based. Thus advertisers only pay when affiliates deliver a specified customer action. In the ecommerce context, this action is typically an online purchase, which makes affiliate marketing very cost effective.
To start off, run one in-house using an app like Affiliatly, GoAffPro, Enlistly, LeadDyno or Refersion.

https://apps.shopify.com/search?q=Affiliate