Hey Devs, This is the most complete and well-structured HTML cheatsheet you can find online!!
So let's start.

Basic Tags

<html> </html>
 - Creates an HTML document
<head> </head>
 - Sets off the title & other info that isn't displayed
<body> </body>
 - Sets off the visible portion of the document
<title> </title>
 - Puts name of the document in the title bar; when
bookmarking pages, this is what is bookmarked

Formatting

<p> </p>
 - Creates a new paragraph
<br>
 - Inserts a line break (carriage return)
<blockquote> </blockquote>
 - Puts content in a quote - indents text from both sides
<div> </div>
 - Used to format block content with CSS
<span> </span>
 - Used to format inline content with CSS

Body attributes

<body bgcolor="?">
 - Sets background color, using a name or hex value
<body text="?">
 - Sets text color, using name or hex value
<body link="?">
 - Sets color of links, using name or hex value
<body vlink="?">
 - Sets the color of visited links, using a name or hex value
<body alink="?">
 - Sets the color of active links (while mouse-clicking)

Lists

<ul> </ul>
 - Creates an unordered list
<ol start=?> </ol>
 - Creates an ordered list (start=xx, where xx is a counting number)
<li> </li>
 - Encompasses each list item
<dl> </dl>
 - Creates a definition list
<dt>
 - Precedes each definition term
<dd>
 - Precedes each definition

Text Tags

<pre> </pre>
 - Creates preformatted text
<h1> </h1>
 --> 
<h6> </h6>
 - Creates headlines -- H1=largest, H6=smallest
<b> </b>
 - Creates bold text (should use instead)
<i> </i>
 - Creates italicized text (should use instead)
<tt> </tt>
 - Creates typewriter-style text
<code> </code>
 - Used to define source code, usually monospace
<cite> </cite>
 - Creates a citation, usually processed in italics
<address> </address>
 - Creates address section, usually processed in italics
<em> </em>
 - Emphasizes a word (usually processed in italics)
<strong> </strong>
 - Emphasizes a word (usually processed in bold)
<font size=?> </font>
 - Sets size of font - 1 to 7 (should use CSS instead)
<font color=?> </font>
 - Sets font color (should use CSS instead)
<font face=?> </font>
 - Defines the font used (should use CSS instead)

Graphical elements

<hr>
 - Inserts a horizontal rule
<hr size=?>
 - Sets size (height) of horizontal rule
<hr width=?>
 - Sets width of rule (as a % or absolute pixel length)
<hr noshade>
 - Creates a horizontal rule without a shadow
<img src="URL" />
 - Adds image; it is a separate file located at the URL
<img src="URL" align=?>
 - Aligns image left/right/center/bottom/top/middle (use CSS)
<img src="URL" border=?>
 - Sets size of border surrounding image (use CSS)
<img src="URL" height=?>
 - Sets height of image, in pixels
<img src="URL" width=?>
 - Sets width of image, in pixels
<img src="URL" alt=?>
 - Sets the alternate text for browsers that can't process images (required by the ADA)
<a href="URL">clickable text</a>
 - Creates a hyperlink to a Uniform Resource Locator
<a href="mailto:EMAIL_ADDRESS">clickable text</a>
 - Creates a hyperlink to an email address
<a name="NAME">
 - Creates a target location within a document
<a href="#NAME">clickable text</a>
 - Creates a link to that target location

Forms

<form> </form>
 - Defines a form
<select multiple name=? size=?> </select>
 - Creates a scrolling menu. Size sets the number of menu items visible before user needs to scroll.
<select name=?> </select>
 - Creates a pulldown menu
<option>
 - Sets off each menu item
<textarea name=? cols="x" rows="y"></textarea>
 - Creates a text box area. Columns set the width; rows set the height.
<input type="checkbox" name=? value=?>
 - Creates a checkbox.
<input type="checkbox" name=? value=? checked>
 - Creates a checkbox which is pre-checked.`
<input type="radio" name=? value=?>
 - Creates a radio button.
<input type="radio" name=? value=? checked>
 - Creates a radio button which is pre-checked.
<input type="text" name=? size=?>
 - Creates a one-line text area. Size sets length, in characters.
<input type="submit" value=?>
 - Creates a submit button. Value sets the text in the submit button.
<input type="image" name=? src=? border=? alt=?>
 - Creates a submit button using an image.
<input type="reset">
 - Creates a reset button

HTML5 input tag attributes

<input type="email" name=?>
 - Sets a single-line textbox for email addresses
<input type="url" name=?>
 - Sets a single-line textbox for URLs
<input type="number" name=?>
 - Sets a single-line textbox for a number
<input type="range" name=?>
 - Sets a single-line text box for a range of numbers
<input type="date/month/week/time" name=?>
 - Sets a single-line text box with a calendar showing the date/month/week/time
<input type="search" name=?>
 - Sets a single-line text box for searching
<input type="color" name=?>
 - Sets a single-line text box for picking a color

Tables

<table> </table>
 - Creates a table
<tr> </tr>
 - Sets off each row in a table
<td> </td>
 - Sets off each cell in a row
<th> </th>
 - Sets off the table header (a normal cell with bold, centered text)

Table attributes

<table border=?>
 - Sets the width of the border around table cells
<table cellspacing=?>
 - Sets the amount of space between table cells
<table cellpadding=?>
 - Sets the amount of space between a cell's border and its contents
<table width=?>
 - Sets the width of the table in pixels or as a percentage
<tr align=?>
 - Sets alignment for cells within the row (left/center/right)
<td align=?>
 - Sets alignment for cells (left/center/right)
<tr valign=?>
 - Sets vertical alignment for cells within the row (top/middle/bottom)
<td valign=?>
 - Sets vertical alignment for cell (top/middle/bottom)
<td rowspan=?>
 - Sets number of rows a cell should span (default=1)
<td colspan=?>
 - Sets the number of columns a cell should span
<td nowrap>
 - Prevents lines within a cell from being broken to fit
Hope this helped and thanks for reading!
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Also published at https://dev.to/garvitmotwani/html-cheat-sheet-the-most-useful-html-commands-3ha5