This post is specially designed for my sweetheart:)
I will try to explain it as easy as possible:)
For every html page, you can treat it as a kind of documents. Hence, we have to start every page with <!DOCTYPE html> to define the type of document.
In HTML5 coding, the commands always start with
<!DOCTYPE html>
<html> <!-- For a basic html page, it contains a head and a body -->
<head>
<title>Page Title</title> <!-- This is where you define the title and other features in the page -->
</head>
<body>
<h1>This is a Heading</h1> <!-- <h> is a command to define the header of a paragraph -->
<p>This is a paragraph.</p> <!-- <p> is a command to define the content of a paragraph -->
</body>
</html>