All files needed can be downloaded at the above website.
This is a quick way to check any iOS device, on any firmware, and see what SHSH your device has on file.
IF you have SHSH saved for a particular firmware, this means you can always downgrade to this firmware, as Apple does not allow you downgrade to any firmware, they only allow you to run their current version.
This is handy, as there is no untethered jailbreak for iOS 5 and a lot of people are looking to go back to a untethered jailbreak by downgrading to 4.3.3, which is supported by the untethered jailbreak.
You're device does not have to be jailbroken for this to work, this will work with any iPhone, iPad or iPod running any firmware.