Search engine optimisation indicates "Search Engine Optimization". It signifies a set of techniques and best techniques aimed toward bettering the visibility of a web site on search engines.   You specify the first URL because the search engine might have issues deciding which a person should be the main URL.  https://www.presta-addons-modules.com/en/seo/prestashop-seo-automatic-hreflang-tags-canonical-tags-on-all-pages.html