ALL Web sites use HTML to one degree or another.
HTML files consist of the text, images, and other elements to be displayed on the page. Other tags are used to insert elements such as forms, images, animation, multimedia, etc. HTML is relatively easy to learn and well within the realm of non-programmers. Web development tools which will create the HTML for you based on how you layout a page. Even if you use one of these tools, it is helpful if you understand a little HTML to give you more control over the development process.