Pointing subdomains to their appropriate resources requires a server configuration - and so there is no one, sinlge answer beyond that - the details are different for different servers.
Some web hosting firms provide a wizard for their clients that allows you to set up sub-domains through a simple interface. If that's your situation (check with hosting company) the process should be painless.
Some people will need to know the specific details for configuring their server at the admin level - that information will be in the server documentation, if the hosting support/IT dept/person doesn't already know how to do it.
These links to Google searches will give you a list of threads here on WebmasterWorld for two general categories of servers:
Microsoft IIS Servers [google.com]
Apache Servers [google.com]
Thanks taking the time to answer this. My webhost allows me to add subdomains quite painlessly as you pointed out.
I have just added a subdomain say bananas to fruitstore.com so that I get bananas.fruitstore.com
also I have named the web directory as www/fruistore/fruits where the bananas htm filed is stored.
Trouble is what else do i need to do?
Is there a good book on making these kinds of changes to a website?
Can you help?