Getting and applying an SSL cert (from CAcert.org) to an nginx server on Raspberry Pi

Question

I want to enable https on a web server.

Environment: validated domain on CAcert.org. Server certificate generated there. Target server: a PiStar (running on RaspberryPi using nginx as the web server).

I started following this https://discourse.pi-hole.net/t/enabling-https-for-your-pi-hole-web-interface/5771 but they do not explain how to get the cert.

I want to download a cert from CAcert.org. I have found an older post but it skips a description of how to set up the encryption and any details on getting the cert. Other sites so far found make assumptions, and use jargon I don't understand and skip steps.

email back from CAcert includes this

If you have not imported CAcert's root certificate, please go to: https://www.cacert.org/index.php?id=3 Root cert fingerprint = A6:1B:37:5E:39:0D:9C:36:54:EE:BD:20:31:46:1F:6B Root cert fingerprint = 135C EC36 F49C B8E9 3B1A B270 CD80 8846 76CE 8F33

What am I supposed to do on that page ?