Structured data21 is code that you can add to your sites' pages to describe your content to search engines, so they can better understand what's on your pages. Search engines can use this understanding to display your content in useful (and eye-catching!) ways in search results. That, in turn, can help you attract just the right kind of customers for your business.
The caveat in all of this is that, in one way or another, most of the data and the rules governing what ranks and what doesn't (often on a week-to-week basis) comes from Google. If you know where to find and how to use the free and freemium tools Google provides under the surface—AdWords, Google Analytics, and Google Search Console being the big three—you can do all of this manually. Much of the data that the ongoing position monitoring, keyword research, and crawler tools provide is extracted in one form or another from Google itself. Doing it yourself is a disjointed, meticulous process, but you can piece together all the SEO data you need to come up with an optimization strategy should you be so inclined.
The terms SEO experts often start with are page authority (PA) and domain authority (DA). DA, a concept in fact coined by Moz, is a 100-point scale that predicts how well a website will rank on search engines. PA is the modern umbrella term for what started as Google's original PageRank algorithm, developed by co-founders Larry Page and Sergey Brin. Google still uses PageRank internally but has gradually stopped supporting the increasingly irrelevant metric, which it now rarely updates. PA is the custom metric each SEO vendor now calculates independently to gauge and rate (again, on a scale of 100) the link structure and authoritative strength of an individual page on any given domain. There is an SEO industry debate as to the validity of PA and DA, and how much influence the PageRank algorithm still holds in Google results (more on that in a bit), but outside of Google's own analytics, they're the most widely accepted metrics out there.

QUOTE: “Search engine optimization is often about making small modifications to parts of your website. When viewed individually, these changes might seem like incremental improvements, but when combined with other optimizations, they could have a noticeable impact on your site’s user experience and performance in organic search results.” Google Starter Guide, 2008
QUOTE: “Shopping or financial transaction pages: webpages which allow users to make purchases, transfer money, pay bills, etc. online (such as online stores and online banking pages)…..We have very high Page Quality rating standards for YMYL pages because low-quality YMYL pages could potentially negatively impact users’ happiness, health, or wealth.“
However, that’s totally impractical for established sites with hundreds of pages, so you’ll need a tool to do it for you. For example, with SEMRush, you can type your domain into the search box, wait for the report to run, and see the top organic keywords you are ranking for. Or, use their keyword position tracking tool to track the exact keywords you’re trying to rank for.