The game is basically the direct successor to Stronghold 1, a real-time strategy game that is all about building a working economy and killing the opposing lords of the castles. So it is located in the time of castles and knights. Special emphasis was placed on a realistic economy.
With this game it is no problem to buy it on Ebay or Amazon or from a retailer. The game is also available at Steam, but in a Stronghold package that contains some other Stronghold games, as well. The HD version is available at GOG.
Basically just install straight forward. The offer to install GameSpy can be refused confidently, because the GS servers are now permanently offline. There is also a patch 1.1 in circulation, which patches the game, but at the same time gives it back the CD query. That's why one might want to avoid it. Once you've installed SHC, it's usually enough to simply copy the already installed game. So if you reinstall Windows or redistribute it, no new installation is necessary.
For SHC, when creating a server yourself, you need to open ports 2300-2400 (TCP + UDP) and 47624 (TCP). The game can also be played directly over the Internet, with IP address then. On the LAN, it usually finds open games by itself. Gamespy can be omitted because the servers no longer exist.