HTML is an acronym and stands for Hypertext Markup Language. This is the format that websites are written in. This means that the basic structure of a website is written in HTML, and is then interpreted and shown by a web browser like Firefox. The creator of a website writes their text in an HTML file. This text can then be structured and formatted with HTML. In addition, HTML is used to build links to other websites into the text, and to incorporate images, videos or background melodies.
Browsers like Chrome, Firefox, Safari or Internet Explorer read the HTML file and display it graphically. Many HTML files are no longer written by people, but instead by graphical interfaces in the form of content management systems like WordPress or Typo3.
HTML documents don’t need elaborate text programs
Early websites were developed completely in HTML. CSS also established itself for modern web design through the increasing dynamism on many internet sites. HTML only serves the structure of a website, for example it determines whether a text should appear as a heading or as a body of text. A linked CSS file will then define what format the section of text should have.
An HTML document can be written in any text program. A simple website can, if desired, only be created with a PC running Windows. You do not need any complex software for a simple website. The HTML document contains the text that should appear on the website and the tags, or markup elements, which define and structure the document.
You can find more information on HTML on Wikipedia: https://en.wikipedia.org/wiki/HTML
and on the official manufacturer’s website: https://www.w3.org/html/