MAKE SURE YOU ARE CONNECTED TO THE INTERNET!!!!
Download the latest version of redsn0w.
Follow the on-screen instructions to put iphone in DFU mode.
Let the process be completed.
Let the process be completed untill it says done
Now its ok to disconnect your iphone the rest of the process will be completed on the iphone.
Enjoy!! Your iPhone is jailbroken now.
If you are facing any problem then please see the video below or comment below.