Your browser receives HTML, CSS and other files from the web server where the site is hosted. The browser interpets the data and creates a page you can access. The rendering also places video, audio and interactive elements on the page.
There is one fundamental language on the web, and two others that support and expand it extensively. These are HTML, CSS, and Javascript. We'll discuss the specifics of these over the next week, but this is a broad overview.
Hypertext Markup Language, referred to as HTML, is the fundamental language of the web. You can think of it as the "skeleton" of a website. It declares the structure of a page and contains the text. This very page you're reading now is written in HTML, as are all webpages you've read.
CSS, or Cascading Style Sheets, is a presentation language. It's used to style websites. It also assists web developers and designers in layout and manipulation of elements on a page. If HTML provides a skeleton, CSS is the skin.
Javascript is a high level (close to human language) programming langauge that gives developers and designers dynamic control over a website. The code is executed locally in your browser, and gives users the ability to create deeply intractive online experiences. If HTML is the skeletoin, and CSS the skin, Javascript is the brain/nervous system of the web.
What is HTML?