It’s also important to understand that “renewal” just means issuing a new certificate. It doesn’t change the expiry of the old certificate. The new certificate needs to be installed in or accessible to your web server in order to be used by it.
if you’re using Certbot on your web server and have pointed the web server at the version of the certificate in /etc/letsencrypt/live, this should be handled for you automatically. If you had to do some kind of certificate import step or if you made a separate copy of the certificate, you would have to repeat that process for every renewal.