Detail about how to jailbreak your iPhone

First of all you will need to know what iPhone can be jailbroken and what cannot jailbreak
iPhone 3G, 3GS can run a jailbroken iOS 4.1 only you have your iphone jailbroken on your previous version.
---> This can be done by using Sn0wbreeze 2.0.2
iPhone 4 on iOS 4.0.2 n 4.1 cannot yet jailbreak


ALL iDevice on 4.0.1 or below can be jailbreak by using JailbreakMe Star