Netplan is the YAML layer that configures networking on Ubuntu Server: you describe addresses, routes and DNS in one file, and a generator renders that into config for systemd-networkd. This crash course is written for a dedicated box with a static public IP, no Wi-Fi, and SSH as the only way in. It covers where the files live, the root-only 600 permission rule, a full static IPv4 and IPv6 example, the generate, try and apply commands that stop you locking yourself out, plus VLANs, bonds, bridges, and the cloud-init file that keeps overwriting people's edits.