Confused about the block editor’s HTML compared to using PHP

Back in 2013 I had a WordPress website where I created a custom theme, had a database, and then had some custom design. It used to be a sort of database with images taken from movies.

I'm not a developer and have completely forgotten everything at this point, but I really wanted to get this old site up a running again, but this time with a more modern design and efficient code.

So I have been watching a few tutorials and everything seems to be revolving around the new block editor which uses HTML-files instead of PHP. I must admit that I have difficulties learning how to understand and code for this editor.

Been spending some time with the theme.json file to style things. After that I wanted to start building the site design, but using HTML leaves me with a lot of questions:

• How do I have dynamic paths to assets/images to fetch images?
• How can I create "loops" to fetch content from the database?
• What parts of the styling and settings should be kept in the theme.json file rather than in the style.css?

There are a ton of questions and currently my main problem is how to structure the website and then fetch content dynamically from the database (still need to set this up though).

Anyone have any good tutorials for complete beginners, or any ideas where to start?