What is Certbot?
Certbot is a free, open source software tool for automatically using Let’s Encrypt certificates on manually-administrated websites to enable HTTPS. -https://certbot.eff.org/pages/about
Installing Certbot
Requesting a Certificate
NOTE: In order for Let's Encrypt to verify ownership of the DNS name, the host certbot is running from must be accessible via port 80 (http) or port 443 (https). For homelab users, this will normally involve port forwarding from the router to the certbot host, which is beyond the scope of this tutorial. Just note, I have forwarded port 80 on my router to the host running certbot for this handshake to complete successfully.
Source: https://certbot.eff.org/instructions?ws=webproduct&os=windows