SSL is a security technology which ensures sensitive data like passwords and credit cards are sent securely between your website and visitors. If you have SSL enabled, it is also very important to ensure that your page is actually forcing usage of HTTPS by redirecting from a non-secure HTTP version to secure HTTPS version. Not doing this means users and Search Engines may continue to access insecure versions, which can also reduce your ranking ability.
Often systems like Wix or Shopify will make it easy to enable, and redirect to SSL versions. If you have Wordpress, or a custom built site, you may require a developer's involvement to ensure that pages are being redirected to their new HTTPS versions. This can be done within a site's configuration or htaccess rules.