Introduction
HTML is the language that your browser reads when it shows you a webpage. It is a variant of XML. It makes the actual content that you see, but also can contain visual styling information (typically in the form of an external CSS file) and also can have an in-browser (client-side) programming language called JavaScript.
Bare Minimum Example
<!DOCTYPE html>
<html>
<head>
<title>Minimal</title>
</head>
<body>
<p>Hello World!</p>
</body>
</html>
Tag Structure
Tags are put on either end of something to describe the content between the tags. Since HTML is visual, think of a tag as a box drawn around whatever is inside of it. The outermost tags are <HTML>, <HEAD>, and <BODY>. The <HTML> tag simply says that the contents are HTML. It is the very outermost box on the screen. The <HEAD> tag is invisible. It summarizes the contents (like title and keywords) and also lists files the page needs like stylesheets and scripts - both of which can alternatively be embedded into the actual HTML file if desired instead of being a seperate file. The <BODY> tag is where the actual content that you see on in the browser window goes. It can contain images, text, and other containers.