Structured data is a machine-readable summary of what a page is about, written in JSON-LD — the format Google explicitly recommends over Microdata and RDFa. This tool builds one valid block per type, includes only the properties you filled in, and escapes the output so it can't break out of the script tag it gets pasted into.
Two checks are worth running after you paste it: the Schema Markup Validator on this site confirms the block parses and declares a type once the page is live, and Google's own Rich Results Test confirms the per-type property requirements for the specific enhancement you're after. Keep the markup honest — describing products, ratings, or events that don't match what a visitor actually sees on the page is a manual action risk, not a clever trick.