This is step-by-step instructions on how to perform jailbreak of your iPhone 3GS on iOS 4.3.5 firmware using RedSn0w 0.9.8b7b for Mac OS.
If you have iPhone 3GS with an old bootrom version 359.3, the jailbreak is untethered. If your device has bootrom version 359.3.2 and higher, jailbreak will be tethered. You can detect your bootrom version using this tutorial.
Tethered jailbreak means that each time you restart your device you will need to connect it to a computer and run redsn0w.
If you have other device, here are links to our RedSn0w 0.9.8b7b iOS 4.3.5 jailbreak tutorials: