HTML

Not a programming language: a markup language. Believe it or not, you could build websites using only HTML. It would be light and fast, easy to maintain by a designer without the need of a programmer, SEO-friendly, easy to cache, and it forces you to think of the content first. Why then all websites are so heavy and slow?

• They use libraries and frameworks they don't need
• They have useless/annoying features (ads, sign-up pop-ups, chat panel, responsive hamburgers menu)
• They have lots of trackers (Google analytics, screen replay, Mixpanel, pixel trackers, cookies)
• They don't optimize images/videos
• They have lots of browser and resolution specific code
• They use huge blog CMS and generators

All website will anyway end-up being HTML, so it's worth learning it properly. HTML5

HTML define the "structure" of the page, if a section is a title, a paragraph, a footer, a generic container, etc.

on jsbin.com

There are less than a hundred usable tags in HTML. But you can easily survive with a smaller subset:

<!--...-->    Defines a comment
<a>    Defines a hyperlink
<br>    Defines a single line break
<p>    Defines a paragraph
<pre>    Defines preformatted text
<h1> to <h6>    Defines HTML headings
<iframe>    Defines an inline frame
<img>    Defines an image
<div>    Defines a section in a document
<span>    Defines a section in a document

<form>    Defines an HTML form for user input
<input>    Defines an input control
<button>    Defines a clickable button
<select>    Defines a drop-down list
<option>    Defines an option in a drop-down list
<textarea>    Defines a multiline input control (text area)

<ul>    Defines an unordered list
<li>    Defines a list item

<table>    Defines a table
<td>    Defines a cell in a table
<th>    Defines a header cell in a table
<tr>    Defines a row in a table

<canvas>    Used to draw graphics, on the fly, via scripting (usually JavaScript)

<link>    Defines the relationship between a document and an external resource (most used to link to style sheets)
<style>    Defines style information for a document
<script>    Defines a client-side script

HTML tags have attributes, like the "src" attribute of the "img" tag:

<img src="image.png">