Setting up a reverse proxy

Setting up a reverse proxy but I cannot figure out some DNS settings, hoping someone may help.

Following this guide: https://www.youtube.com/watch?v=nmE28_BA83w&t=174s

I get lost at 4:16 because I have no idea what mines are. I’ll try again tomorrow but was hoping someone may know a quick way to figure these YAML file configs.

I have spent a week straight trying to figure it out on my own and googling, since I know this will power my RP5, nas, and other self hosted services.