Hugo uses Markdown for its simple content format. However, there are a lot of things that Markdown doesn’t support well. You could use pure HTML to expand possibilities.
But this happens to be a bad idea. Everyone uses Markdown because it’s pure and simple to read even non-rendered. You should avoid HTML to keep it as simple as possible.
To avoid this limitations, Hugo created shortcodes. A shortcode is a simple snippet inside a page.
Hugo-theme-learn provides multiple shortcodes on top of existing ones.