Your Server
Any Ubuntu machine Cloudgate reaches over SSH, or the machine Cloudgate itself runs on. A Setup run installs Docker Swarm and Traefik, and Domains get Let's Encrypt certificates.
Bought Server. On the Hosted instance, buy one in the console: pick a location on a world map and a size, add backups or extra storage from 10 GB to 10 TB. It is billed monthly in advance on the same invoice, at the price shown before you buy.