The easiest is if it provides you with an installation file. You might recognize if that is the scenario if it finishes in _theme.ocmod.zip. In that situation, all you should do is drop by Extensions > Installer A lot of them come with features including Ajax lookup, product quick view, https://www.presta-addons-modules.com/en/opencart-seo-automatic-google-rich-snippets-json-ld-integration-opengraph-twitter-tags-schemaorg.html