First of all, make sure your device runing iOS 5.0 or 5.0.1.
To update to iOS 5.0.1, download the IPSW for your device here:
Now, connect your device to iTunes and click Check for update button at the same time with the Shift button.
After update, Jailbreak your device:
Step 1:
Step 2:
Make sure the iTunes is closed, and run Absinthe.
Step 3:
Connect your device to computer, make sure it is open and click the Jailbreak button in Absinthe. Now, wait to Jailbreak.
Step 4:
When Jailbreak finish, the Absinthe icon is installed to your home screen. Touch it, and whait a moment. Now, the Absinthe will close auto and the Absinthe icon is replaced with Cydia!