I'm pretty sure you're trolling.
But if you're not...
Cydia is not a jailbreak. Cydia is the app that the jailbreak installs on your device.
Cydia works like the AppStore, except it contains non-Apple Approved apps.
Either use greenpois0n or limera1n to jailbreak iOS 4.1. It's just down to personal choice to which one you use, really. They both use the same exploit.
If you have an iPod touch 2G MC model, use greenpois0n.