(Jailbreakme is not valid for latest iOS i.e.4.2.1)
Step 1:
Make you your iPhone is backed up in iTunes, in case something goes wrong.
Step 2:
From you iPhone, go to JailbreakMe.com.
Step 3:
Slide to jailbreak.
Step 4:
Sit back, relax. JailbreakMe will be downloaded to your iPhone and will work its magic. When done, a pop up will tell you that Cydia has been installed.
Step 5:
Reboot your iPhone. You don’t have to, but it’s always a good thing to do.
That’s it. Nothing to download to your computer.
Heres a video for reference:-
