What is The Mechanism of Back links to rank you website?

While you create your back link in any website that back link will be crawl by the search engine robots and crawler. After that back link will be visible in that search engine. That back link has its own parameters like index or nonindex from that parameter robots or crawler define to index or not to index that back link. Also many other experts tools of seo gives ratting to that website of back link like trust flow, domain authority, page rank etc etc. This all parameter pass the values to your website after creating back link that is depend upon the parameter of back links like dofollow and nofollow.