WordPress custom theme building question!

Hi there. I’m not a professional developer but today find something interesting. I wanna build website theme for wp and know how to do this. But some of functionality for me is unknown.

Example: content block -> different sections -> section content

How I can put different sections inside block editor ?

I can’t post example here of website, but I don’t understand basically how to do this

Example 2:

container(default output content block)
-section1
—h2 and others content
-section2
—h2 and other content

But by default we have container -> some block or content