If you have two articles which is speaks about same thing then you can set canonical url to make that as original article.
For example: consider 2 articles:
By writing two article for the cat, surely the two articles will rank for the keyword "cat" It will create a duplicate content issue. In order to avoid it.
For 2nd article abc.com/ cat-tips in this article you are inserting canonical url abc.com/cat- foods. Which says google to pass all authority to abc.com/cat-foods. So this post will rank alone for the keyword "cat".