Instance: You might have an e-commerce Web page with products internet pages for different sizes of a selected t-shirt.   You specify the principal URL since the internet search engine may have trouble analyzing which a person ought to be the main URL.  The following tutorial will provide you with https://www.presta-addons-modules.com/en/seo/prestashop-seo-automatic-hreflang-tags-canonical-tags-on-all-pages.html