The Scroll Trigger allows you to show campaigns when a particular on page element becomes visible. With this, you can show campaigns at precisely the right time on a page - when a user is deeply interested in a product or blog page, or when they've reached the bottom of a category, for example.
The trigger itself only shows when a certain part of a site comes into view. We can set this up so that anytime a selector (a part of the site, as named in your source code) is visible, your campaign will show.
Firstly, we're going to want to find a selector:
Choose a Selector
The selector is the CSS identifier that you can specify to tell the campaign when to appear. You don't need to know how to code to obtain this and you can do it from your web browser:
Find the part of the site you want your campaign to trigger on and find a universally present element. For the example here, we've used an Add to Cart button - the campaign will trigger when this comes into view. Right click it and hit Inspect. You'll then be presented with the dev tools panel that looks like the below:
From here you'll need to find the parent element (you can do this by seeing if there are any expanded arrows above the element you Inspected, you may already have the parent element). Once done, right click on this in the dev tools panel, scroll to Copy and Copy Selector.
With this done, you can paste the selector back into the box where your Scroll trigger is. Anytime a user sees this element, your campaign will trigger.