<header>...</header>
<nav>...</nav>
<main>
  <article>
    <section>...</section>
  </article>
  <aside>...</aside>
</main>
<footer>...</footer>

• Improves accessibility — screen readers understand page structure
• Improves SEO — search engines weight semantic sections differently than generic divs
• article = self-contained content; section = a thematic grouping within it