HTML: Can I NOT use HTML5 tags while declaring my page to be HTML5?

Beginner question, pardon my ignorance:

Can I NOT use some HTML5-specific tags (ex. <header>, <section>, <aside>, <main>) and still pass my page as HTML5 by declaring so? I've been practicing writing a few basic layouts and reading tons of articles and tutorials. The more I do it, the more I can't help thinking some tags are redundant. For example, why <header> when <h1> <h2>, etc. are headers to begin with? <main> and <section> and <footer> are all supposed to be different, but they all sound to me like a type of "section," so I'm confused. But they all seem to be kind of visual stuff, so why can't just use <div> and <span> for all layout/visual stuff if I am to practice Progressive Enhancement and start with the bare minimum viable contents? To me, it's simpler just to remember two generic tags and say class="footnote" to shape it up after writing a page like a normal barebone writing with just text and images.

People keep telling me how HTML5 is the standard nowadays, so I want to comply, but I am a bit lost on how and when we are supposed to use those tags as many people use each of them slightly differently from others. I thought that maybe I could stick to the most straightforward set of things to mark up my page and avoid usage errors at least for now. Advice?