Spring is an engine for realtimestrategy games. If you want to play games, you have to download Spring (engine) and a game itself. If you want to play, you also need some maps.

Spring games are mostly designed for multiplayer games. At the moment you can also fight against AI Opponents (Bots) but you wont find a real campaign(missions are already being created, so lets hope that this will change soon!).

If you are developer and interested in using spring engine you should visit http://springrts.com/.