You can see all of the information you need to read through beforehand here, the main thing you must know is that ultrasn0w unlockers should not use this jailbreak as it does not allow you to create custom 4.2.1. IPSWs.
There are already well over 1000 comments (here) where people are asking and answering each-others questions, if you are having trouble using redsn0w 0.9.6b4 it is well worth reading this comments as there are plenty of useful tips and how to guides to look at.
Have you successfully used redsn0w 0.9.6b4 to jailbreak your iPhone/iPod Touch/iPad?
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