How to add Structured data to a site? I am trying to find a lot on Google how to add Structured data to site and from all the tutorials I got an impression that there is RDF module in core which was supposed to do that work like providing structured data to search engines (Google).

That module is in core and already installed on site, still Google Search Console saying,


  We do not detect any structured data on your site.


Am I missing something? If RDF does not provide structured data to search engines, what is the right method to add structured data to a site? Please, correct me if I am wrong about RDF.
If you enable the RDF module, Drupal will automatically output some RDFa for your content. You can use a RDFa parser to extract it, e.g., http://linter.structured-data.org/. If it doesn’t find any data (under "Raw structured data extracted from the page"), you are likely using a theme that doesn’t support it. Use a default/core theme for testing, you should see it then.

If you want to provide additional structured data for your content types and field content, you need to map the content types to suitable RDF types, and the fields to suitable RDF properties. If you care about SEO, you’ll likely want to use the types and properties from Schema.org, as the big search engines sponsor this vocabulary, and use it for things like rich search results. 

One way to add these mappings is using the RDF UI module (which comes integrated with Schema.org).