Canonical element is a line of code that you add to pages that may be duplicates. In this code, you designate the “canonical,” or “proper,” URL. Engines will note this URL and apply link popularity and authority to the canonical version instead of applying them to duplicate URLs. This should consolidate the authority and link popularity into a single URL, as opposed to splitting them among several similar URLs.

How Do You Use the Canonical Tag?
The syntax of the new canonical attribute is simple. Between the and tags on your page (title element and meta data), place this line:

<link rel=”canonical” href=”http://www.yoursite.com/correct-url/” />
The actual URL in the line above is for the actual canonical URL that you’ll put in your file.

As an example, let’s assume you have duplicate content issues that result in all of the following URLs resolving correctly, and that the first URL in this list is the “correct” one:

http://www.yoursite.com/correct-url/

http://yoursite.com/correct-url/

https://www.yoursite.com/correct-url/

http://www.yoursite.com/correct-url/default.aspx

http://www.yoursite.com/correct-url/?from=sidenav

and so on…

To apply the canonical element, just add the following line to the section of all pages:
<link rel=”canonical” href=”http://www.yoursite.com/correct-url/” />