To add the AdRoll Pixel to your Shopify store, you need to start by logging into your AdRoll account and finding the Pixel setup instructions. Once you have the Pixel code, log into your Shopify admin dashboard and navigate to the "Online Store" section. From there, go to "Themes" and select "Actions" on your active theme, then choose "Edit code." Locate the `<head>` section in your theme.liquid file and paste the AdRoll Pixel code there. After pasting the code, make sure to save your changes and publish the updated theme. This will activate AdRoll tracking for your Shopify store.