new to this - what is structured data seo?

Extra code on the page (usually JSON-LD) that tells search engines in plain terms what the page is: a product with a price, a recipe, an event, a local business with opening hours. Google uses it for rich results like star ratings or prices under your listing. It doesn't push rankings up by itself, it just makes the listing richer when you qualify. Run the page through Google's Rich Results Test after adding it - small typos in the markup are really common and it'll just silently not work.