The common thing in all redsn0w jailbreak of iOS 6 beta is that all jailbreak can’t install cydia and its tenthered jailbreak.
Have a look at the video posted by iDB, shows how to jailbreak iOS 6 GM with RedSn0w…
Every tutorial is incomplete if its not Step by Step, Let me show you step by step tutorial to jailbreak iOS 6 GM using Redsn0w:
Note: You need the iOS 6 GM firmware to proceed. This jailbreak does not install Cydia.
Step 1: Download RedSn0w 0.9.13dev4 from our downloads page, and run it.
Step 2: Place your A4 device (iPhone 4, iPod touch 4th gen) into DFU mode.
Step 3: Click Extras > Select IPSW > and point to the iOS 6 GM firmware for your device. (You must be a developer to access this firmware).
Step 4: Once the firmware is successfully identified, go back to the main page and click Jailbreak.
Step 5: Make sure that Install SSH is checked, and proceed. Your device will now be jailbroken.
Step 6: Once the jailbreak process is completed, put your device back into DFU mode.
Step 7: Go back to the main page of RedSn0w and click Extras > Just boot. This will perform a tethered boot on your device.
Step 8: You should now be able to access your device via SSH. By this means you can install the necessary things you need to enjoy your jailbroken device as a developer.
with the release of ios 6 to the public we can make sure redsn0w will be updated to install cydia for regular users who aren’t developers.Stay tuned, we will have a full tutorial once that happens.