This is the second line of the xsl styleshhet I am creating. Now, do I need to install this namespace document on my server in order to use it ?
If yes, from where can I download or install it ?
If no, then how will the server understand what a particular tag means ?
If I am using few tags which arer in different namespaces, do I need to al of them on server in order to use the tage specified in them ?
There's no such thing as a "namespace document". A namespace URI is simply a string of characters. Typically it appears to be a link to a web page but it isn't one. It's just a string of characters. XML parsers won't treat it as a link.
You're asking how the server will recognize what an element in that namespace means? Well, it won't. But if -- in the example you posted -- you have an XSLT transformer process that document, it's designed to know what elements in that namespace mean. Other software won't be designed to know that and hence won't be able to understand them.