HTML is used to create web documents through tags that define structure and formatting. There are two types of tags - container tags that define sections of text and empty tags that represent single instructions. Various text editors and WYSIWYG tools can be used to author HTML documents, which have a head and body structure. Graphics, audio, video, and other multimedia can be added through file formats like GIF, JPG, PNG, AVI, MOV, MIDI, and MP3. Additional functionality is provided through plug-ins like Flash, Shockwave, and QuickTime. XML is used to consistently present various data types, while VRML creates 3D virtual reality environments.