Can anybody tell me what is goggle page rank algorithm, please tell me what is the difference between page rank and page rank algorithm and how is this useful for us in promoting our site.
It is the algorithm that computes PageRank. Don't worry too much about Parge Rank, focus on correct SEO for your site (Google it).
Google PageRank algorithm is the way google calculates PageRank, which is based mostly on links pointing to your web site. The more links there are the better your PR will be. Links have to be on pages with not too many other links, they have to be in the right context, they shouldn't be obviously placed just for PR. If you place links on pages that google considers important, you will get more PR. Thats about it.