Schema markup does not directly influence rankings, but it unlocks rich results: review stars, FAQ accordions, recipe cards, event listings, product pricing, breadcrumb trails. Rich results dramatically increase click-through rate from search.
JSON-LD is the format Google explicitly recommends. Markup is embedded in a `<script type='application/ld+json'>` tag, separate from the visible HTML. The most-used types for marketing sites are Organization, WebSite, Article, BreadcrumbList, FAQPage, Product, and SoftwareApplication.
Test every implementation in Google's Rich Results Test before shipping. Schema that validates but is irrelevant to the page content (e.g. fake reviews, mismatched product data) can earn a manual action. Honest, accurate schema is the only kind worth deploying.