For the purpose of this tutorial, javascript is a programming language used for adding features to web pages. It can enhance the dynamic side of your website and make your website interactive for the reader. Its simplicity allows you to confidently use the language without any real audacity, as minor mistakes are usually easily debugged and won't have an impact on the web page itself.
The purpose of this tutorial is to introduce you to javascript, however, you need some background in XHTML in order to proceed - and thereby we strongly recommend that you read Getting Down with XHTML prior to embarking on this tutorial.