OK first of all you don't use the same version of Redsn0w everytime. There are different versions for different firmware ie. 5.0,5.0.1 so go to
iClarified - Apple News and Tutorials and go to Tutorials, iPhone, Jailbreak and look for the method that has the firmware version you are running. It's most likely 5.0.1 if you restored the device, there will ne links in the tutorial for the tools and firmware(ipsw). You don't unzip the file you downloaded rename it from zip to ipsw