Certbox is super easy, all you need is here https://certbot.eff.org/lets-encrypt/ubuntubionic-nginx
For some quick run, just start and you will have wizard running with options to auto create configs for you
sudo certbot --nginx
or if you want to have only certificates and manually add config to nginx files, use this
sudo certbot --nginx certonly
to check it all, use this
sudo certbot renew --dry-run
and have a dry run and current state of certificates.