For general nginx information you might find nginx documentation and https://forum.nginx.org/ helpful.
- Configuring HTTPS servers
- Certbot Instructions | Certbot
- User Guide — Certbot 2.5.0 documentation
- User Guide — Certbot 2.5.0 documentation
- User Guide — Certbot 2.5.0 documentation
For DNS-01 challenge please read Challenge Types - Let's Encrypt
and a list of DNS providers who easily integrate with Let's Encrypt DNS validation