1. First, it tracks changes made to your page's SEO page title and meta description tags.
2. Then it compares the CTR (impressions, clicks) of the page - before and after the change. (Compares 7 days before/after, 14 days before/after and 30 days before/after.)
This is an easy way to know if the changes you (or your SEO team) makes to your on-page SEO tags are beneficial or not. It gets the traffic data from Google Search Console for comparing the before/after impact.