MDN_Document and Structure.
Document and website structure
In addition to defining individual parts of your page (such as "a paragraph" or "an image"),
HTML also boasts a number of block level elements used to define areas of your website
(such as "the header", "the navigation menu", "the main content column").
This article looks into how to plan a basic website structure,
and write the HTML to represent this structure.
Basic sections of a document
Webpages can and will look pretty different from one another,
but they all tend to share similar standard components,
unless the page is displaying a fullscreen video or game, is part of some kind of art project,
or is just badly structured:
heading :
Usually a big strip across the top with a big heading, logo, and perhaps a tagline.
This usually stays the same from one webpage to another.
navigation bar:
Links to the site's main sections;
usually represented by menu buttons, links, or tabs.
Like the header, this content usually remains consistent from one webpage to another —
having inconsistent navigation on your website will just lead to confused, frustrated users.
Many web designers consider the navigation bar
to brather than an individual componente part of the header, but that's not a requirement;
in fact, some also argue that having the two separate is better for accessibility,
as screen readers can read the two features better if they are separate.
main content :
A big area in the center that contains most of the unique content of a given webpage,
for example, the video you want to watch, or the main story you're reading,
or the map you want to view, or the news headlines, etc.
This is the one part of the website that definitely will vary from page to page!
sidebar :
Some peripheral info, links, quotes, ads, etc.
Usually, this is contextual to what is contained in the main content
(for example on a news article page, the sidebar might contain the author's bio,
or links to related articles)
but there are also cases where you'll find some recurring elements
like a secondary navigation system.
footer :
A strip across the bottom of the page that generally
contains fine print, copyright notices, or contact info.
It's a place to put common information (like the header) but usually,
that information is not critical or secondary to the website itself.
The footer is also sometimes used for SEO purposes,
by providing links for quick access to popular content.
(SEO meaning is stands for “search engine optimization.)