This tutorial is a quick one. Cause generating an SSL certificate should be quick and painless anyway.

Add the Source

sudo add-apt-repository ppa:certbot/certbot

Install the generator

sudo apt install python-certbot-nginx

Open Up that port

sudo ufw allow 'Nginx Full'

Don't need the lesser one anymore, Full covers HTTP & HTTPS

sudo ufw delete allow 'Nginx HTTP'

Generate the certificate

sudo certbot --nginx -d example.com -d www.example.com

Follow the onscreen instructions the rest of the way, show the EFF some love, and I recommend redirecting all HTTP traffic to HTTPS when certbot asks. Enjoy!