What part of the docs made you think you needed to use Digital Ocean? They’re one example among many of providers who will give you a virtual Linux server; other examples were mentioned up-topic. I’ve been using Contabo for a while (for Discourse and other sites) and been happy with them.
Now, if you don’t understand “these steps will work on any Docker-compatible cloud provider or local server”, self-hosting your own Discourse instance may be a bit beyond you at this time.