Hi Tarang,
Google is constantly scouring the Web for new content, new websites, and new pages on websites it already knows about. For each site, Google indexes each page that it crawls for future reference, and to be included in search results.
In order for a page to be listed in Google search results, it must first be indexed! When Google's bots crawl a website they create a cached copy of each page, and then adjust their indexes.
It is of course vitally important to have all of the content on your website indexed by Google in order to be included in their search results.
Jul 1, 2014