No idea what " reds0w" to use, ON 3g. (Newbie here)

[smileywork]

Hey, thanks for checking out my thread.

1. I need to know what redsn0w program to use, and why? for a Iphone 3G
2. I have seen so far, that you download 4.2.1 use itunes by(holding shift) to
throw the 4.2.1 on the phone.
3. Then using redsn0w program, and click " Cydia" and Ipad" basband"

So in conclusion, how do i know what version to use on my Iphone 3gs to
unlock and jailbreak it.

thanks,
josh