It's a tracking script that you install on your sales page (the page that receives traffic from your ads). It captures the UTM parameters that arrive with the ad click and automatically passes them to your checkout links, so the sale reaches the platform with the correct source. It also captures Google Ads click IDs (gclid), so it works for both Meta and Google traffic. You can install it in two ways: through Google Tag Manager, by creating a custom HTML tag and pasting the script (the panel has an Insert into GTM button), or by pasting the code directly into the page's HTML. Without the script, clicks that pass through intermediate pages can lose their UTMs before checkout.