How to set up Canonical URLs for categories

Hi,

I want to know how to set up Canonical urls for my product categories. Do I need to fill in the blank box seen here http://traineraddict.com/wp-content/uploads/Picture1.png? If so what exactly do I need to fill it with. The URL I want to give priority to is http://traineraddict.com/product-category/mens-trainers/nike/huarache/

Also if I set this up, will it stop my homepage displaying for some of the same content? http://traineraddict.com/

I very much appreciate any help.

https://wordpress.org/plugins/wordpress-seo/