HTML only defines a set of layout rules for displaying the page. Once you get the feel for creating text documents, you may want to progress to adding some graphics and pictures. HTML provides a simple rules to embed sound and picture links in your page. The picture or audio is actually a seperate file and is not actually inside the document. The server will call up the image file when ever it is needed.
Most browsers can handle a wide variety of image and audio formats.
Its best to stick with the more common ones however. Images in .JPG or .GIF format are the most popular. Audio files are usually in .WAV or .AU format. The fun part comes as you add links to other pages on the net. You may wish to have your pages reference someone elses pages or have them reference yours.