Check out the How to Get Site ID page to get your site ID.

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Surface Tag

Add the following script tag inside your <head> tag: 
<!-- Start Surface Tag -->

<script 
	src="https://cdn.jsdelivr.net/gh/trysurface/scripts@latest/surface_tag.min.js"  
	siteId="YOUR_SITE_ID" // Replace with your site ID
></script>

<!-- End Surface Tag -->

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Surface External Script

Embed the script at the end of the <body> tag: 
<script siteId="YOUR_SITE_ID">
  const surfaceExternalForm = new SurfaceExternalForm();
  surfaceExternalForm.attachFormHandlers();
</script>