Backlink Analysis is important part of SEO. You regularly check your backlinks to make sure that you don't use the same keywords too many times or get the same type of links over and over again. Also, you carry out backlink analysis of your competitors website to find out where they are getting their links. There are a few backlink checkers free to use. Just search free backlink checker and you will find a few. They keep changing to give you a name. Also, people use softwares like Scrapebox. This process of checking the backlinks of sites that are ranking well helps you to understand why they are ranking so that you can do what they did.