If you happen to have duplicate content on your website, search engines will not know which one to show in their results. This is why you need to pick one as the original and set a canonical URL on all the other pages pointing to the original.

This you do by using a canonical tag (rel=”canonical”) in a piece of code that looks like this <link rel=”canonical” href=”www.myoriginalpage.com” /> in each one of the copy pages. As far as the search engine is concerned, this merges all the pages into one.