can anybody explain in detail what is facebook and how it is helpful, what kind of work or business is going on in this..?
Well to start with you might wanna check out the wikipedia for it. Sorry I would post it but I haven't been around for 7 days. The gist is that it is a social netowork where people communicate with friends. There are loads of other features as well most of which you will find on the wikipedia.
I think Wikipedia can do most of the explaining: http://en.wikipedia.org/wiki/Facebook You can create pages for your business, people can like them which will ultimately lead to more traffic and sales.
Just another way of utilizing the massive amounts of traffic FB has. Great for SEO/building traffic/generating a buzz/announcing a product or service/etc.
Make friends and start one or more groups and/or fan pages. Promote your groups and fan pages. Your business will grow as your groups and fan pages grows.
Be social and connect to community. It's a good social media site to generate traffic for your biz and etc.
search on wiki, you can use fb for many purposes, like just interact with your friends 'n familiy and also for your business