How does Google use HTML tags to enhance the search engine?

Question

I know that Google’s search algorithm is mainly based on pagerank. However, it also does analysis and uses the structure of the document H1, H2,

Answer 1

I found it interesting that - with no meta keywords nor description provided - in a scenatio like this:

Some introduction
headline 1
text for section one

Always the "text for section one" is shown on the search result page.