En How to Section Your HTML explican muy bien cómo estructurar una página web con las diferentes etiquetas semánticas que existen en HTML5:
The sectioning elements in HTML5 are <nav>, <aside>, <article>, and <section>. <body> is also kind of a sectioning element since all content lying inside of it is part of the default document section.
Here is a brief explanation of each sectioning element and how they are used:
<nav> – Equivalent to role=”navigation”. Major site navigation that consistently appears frequently across the site. Examples include the primary navigation, secondary navigation, and in-page navigation.
<aside> – Equivalent to role=”complementary”. Content that is only tangentially related (or not related) to the main content. Think of something like a sidebar with supplementary information, a note within an article, or the outer container for a list of related articles at the bottom of a blog post.
<article> – Equivalent to role=”article”. Content that is self-contained in that it makes sense on its own when taken out of context. That could mean a widget, a blog post or even a comment within a blog post.
<section> – Equivalent to role=”region”. Content that needs extra context from its parent sectioning element to make sense. This is a generic sectioning element that is used whenever it doesn’t make sense to use the other more semantic ones.