Installing free Let's Encrypt SSL certificate

First, make sure the domain name points to your server through A records.

Then, execute the following commands, making sure to substitute your real email address and domain names. Repeat -d DOMAIN as many times as necessary.

sudo certbot --nginx --agree-tos --no-eff-email --keep --redirect \
  -m your-email@example.com -d example.org -d www.example.org

You will see a success or failure message, depending on how it went. If it worked, your certificate will be automatically renewed every 60 days.