Hi, please tell me.
What type of factors Google use for given keyword ranking?

I personally think that no body knows how Google actually given ranking towards keyword.I have only idea that always create out the quality backlinks..

Google is a search engine the most popular, and since it focuses mainly on research, we can assume that it does work quite well. From my personal experience I can say that the results of a search query on Google returns more important than other search engines. That's because Google has used a considerable amount of research time in the evolution of more efficient technologies for a search engine efficient and useful.

They just consider how many there are behind those keywords.More sites pointing that keyword means more good ranking for those keywords by google.

Google gives rating to keywords on the basis of how your sites are getting backlink, what is the quality of the backlink you are getting and is that web-site providing backlinks relevant to your niche or not. It also based on the keyword content on the page, in the meta tags combined with the inbound links to the page and the keywords used in the anchor texts of those links.