What do I actually use to design/configure HA?

Brand new to HA. Probably an extremely stupid question.

I have a Thin Client to run HA. After it’s all up and running on the Thin Client, am i supposed to design and configure everything using the Thin Client itself connected to a monitor going forward? Or should I be remotely logging into HA via my regular desktop?

Start a browser on any device on your network and visit http://homeassistant:8123

Your thin client will be the server than runs HA 24/7, where it will monitor and control all the devices you will set up. You don’t access HA from the server itself, but as Wally said, from any other device on your network, in a regular browser by using the IP address.