How Daemons can be usedDaemons usually handle tasks that require no user intervention, and consume low CPU power. CPU-intensive background tasks are not typically termed daemons, as bringing down computers to a sluggish performance can be hardly satisfying for any user, but decreasing the priority of these tasks can qualify them for that without sacrificing their performance, since CPUs are normally idle more than 90% of their time.
A daemon usually handles a single task, and accepts commands through means of IPC (Inter-Process Communication), which you will be briefly exposed to in this tutorial. Tasks handled by daemons include serving web pages, transferring emails, caching name service requests, logging, and for the purposes of this site, serving game clients.
Daemon game servers handle incoming game requests through a network, process these requests, update its persistent storage (database or flat files), and finally sends back responses to the clients. A major issue with game servers, among other servers, is that clients cannot be trusted, since a modified or reverse engineered version of the client can wreck havoc if the server is not ready to handle it. This enforces that clients should not keep a copy of the current game data, they should only send actions, not states, to the server, which would in turn validate those actions, and update the game status.