Canonical Tag is essential as it tells the crawler robots, which link ought to be indexed for a web page which may be open through numerous URLs. Since its introduction in 2009, the  Url has been greatly accepted by webmasters.
Canonical link tag or element demonstrates to Google and other web indexes that one specific Link is the preferred  URL for indexing of a web page despite the fact that it is accessed by multiple URLs. Canonical Tag  is a useful instruction for search engines to deal with duplicate content problems.

You may think these almost the same as they are taking you to a similar page. However, a crawler can't tell that every one of these YRL is for a similar page. In this way, search engine like Google and Bing index each one of them and treat all as duplicated content.

If Google and other search engines find duplicated content then your blog will be punished. This implies you will lose your page rank and search engine positioning. To avoid this your blog must utilize it in their blog as you see the  URL tag helps to avoid duplicate content on your blog.

How to add a Canonical Tag in Blogger?

  • Go to  Blogger Themes
Go to  Blogger Themes
  • Go to edit  HTML 
  • Search (Ctrl+C)  for the following code
 <b:include data='blog' name='all-head-content'/>

If it’s found, that means your template supports Canonical Tag already (actually, Blogger does it automatically for you).

If the line is not found, then you have to add the  Canonical Tag manually. Just add the following code before the </head> tag:

<link rel='canonical' expr:href='data:blog.url'/>