Since WordPress 5 blocks are a fundamental change to the way you create content. Instead of writing paragraphs and headings and adding media, you will now use blocks.
There are 5 theme specific blocks you can use, all found in the Widget section. They are:
Contact Form, Testimonials, Text toggles, Posts Grid and Sitemap:
Some of the theme blocks have controls. For example, these are the controls for the Text toggles: