what is SEO? What are its benefits? And how does it helps a website?

[Lalit]

Search Engine Optimization (SEO) is to make your site search engine friendly. Whenever you go to the internet and want to search for something (because you want to find out what all are available) you enter your search string (or whatever you want to search).You get a series of results displayed and you review these results (probably explore the result that you find interesting!)
How do you make your site appear near the very top (if not on the top position) requires some work and that is called SEO.
Typical search engines available in the world are Google and Bing and you make your site compatible (searchable/crawl able or whatever) to these search engines so that they may list results relating to your website ahead of others