Jailbreak your iDevice  
>> Choose your Firmware : 3.1.2 / 3.1.3 / 4.0 / 4.0.1 / 4.1 / 4.2.1)



Here is all my tutorials regarding Jailbreak in general. 

For specific tutorials regarding how-to basic operations like install .deb files, make a ringtone, use SSH, find IPA, restore a firmware, etc... follow this guide.
For specific tutorials regarding Cydia and tips, cracked and free applications, follow this guide.


Following these guides, you will be able to :

JAILBREAK

UNLOCK

DFU and RECOVERY MODES

FIRMWARES



ITUNES


BASEBAND
Downgrade Baseband 2.10.04 to 1.59.00 (iPhone 4)