Case in point: You may have an e-commerce website with item webpages for different dimensions of a selected t-shirt.   You specify the first URL as the search engine can have problems analyzing which one needs to be the key URL.  The next tutorial will show you the best way https://www.presta-addons-modules.com/en/seo/prestashop-seo-automatic-hreflang-tags-canonical-tags-on-all-pages.html