All website source code can be split up into the following sections: The entirety of the page (HTML), the HEAD(er), and the BODY.

These sections are split up in code as follows....

And that's pretty much it. Now let's describe further what you might see in some of those sections....

head - most likely what you will see in those sections is the code for the metadata used by search engines (Google, Yahoo!, Bing, etc) to add your site to their listings. It also includes code for your favorite's icon (a unique icon that turns up in the navigation bar of your web browser, and when you save it as a favorite) for your site, code for the colors of various elements, and font types and sizes for various elements (or referncing CSS Stylesheets for such).

body - This section deals with the actual CONTENT on the page, this includes your navigation system, pictures, embedded media (videos, music, etc.), and of course, all the text for people to read.

html - are just endcaps for the code in these sections - to tell the web browser this is an HTML document.

But that's not enough to make it come up in a web browser. If you just launch a program, say NOTEPAD.EXE in Microsoft Windows, and then save as the default file type, it's going to open in NOTEPAD next time -as it will save as a "plaintext file" rather than an "html file". The reason is that file extension at the end of the file name - all computer files have a file name, and a file extension except in rare cases or if you are using Linux or Apple. These files are saved as *.HTM or *.HTML files. Both open in a web browser.

So why are there TWO workable extensions for web browsers reading HTML? Well, let's talk computer history briefly.

The dominant computer in business, has been the IBM PC, but Linux systems (and Unix) have been the backbone of the internet since it's inception as the "arpanet" in 1969.

When the IBM PC was created in 1981, it ran a little operating system known as PC-DOS, or better known as MS-DOS - which was a 16-bit operating system with a file naming limitation called the "8.3 rule" or "eight dot three". Basically put, filenames in DOS could only be eight characters long, and the file extentions only THREE characters long. Well, a "mypage.html" file cannot be stored as "mypage.html" - neither on a MS-DOS system, nor in a Windows 1/2/3/9x system either. Because even after "long filenames" became a thing in Windows 95, the 3 letter extension was still a limitation, at least for a time. So you could not create a full "HTML" extension at the end of your webpages. Linux/Unix could.

Hencefourth why I'm linking this on the vintage pages as well - because you CAN create websites on an antiquated PC running anything, even an 8088 at 4.77MHz, even the original PC, and they will parse as long as the website does not use secure HTTP on older browsers (ie https). You could make an entire website using EDLIN if you wanted to - though I don't know why anyone would! You'd need a few bottles of Ibuprofen to survive that one.