The net pages you see on screen usually contain text and images: although some include audio and video. They're created by a set of instructions which has three parts: the content, the way the content looks, and what the content can do, achieved by using:

html
a style sheet
javascript

HTML

HTML is a language that formats the content. Every formatted item is enclosed by two tags. For example a paragraph is enclosed by the tags <p> and </p>: one opening tag and one closing tag. The tags separate the text from other text and add a blank line.

However, if you want the paragraph to use a coloured italic font aligned to the right, the tag has to include extra instructions: repeated in full every time you use the tag.

Most of the instructions don't allow user interaction, although you can submit a form to another person, click a link to another page, and make selections from a list.

HTML is a fixed programming language: you can't invent new tags. It's been changed and expanded over the years, and is currently known as version 4.01. It's not case-sensitive, but it's usually written in lower case as it makes typing simpler.

CASCADING STYLE SHEETS

A cascading style sheet, usually just called a style sheet, includes detailed formatting instructions. Each instruction is a given a name so that it can be re-used often. The advantage is that changing one instruction in a style sheet affects every occurence of it throughout a collection of net pages: saving a lot of repeated code.

JAVASCRIPT

JavaScript allows the content to do something, like change, move, or disappear. As with style sheets, one instruction can be simply re-used.