Many iPhone or iPod touch users use the blackra1n software to jailbreak. The blackra1n jailbreak app was created by geohot, and people use it to install Cydia, install iPhone themes, third party apps not available on the App Store, or unlock their iPhone. Unfortunately geohot named the program blackra1n with a "1" in it. When people tell there friends to use "blackra1n" they will search for "blackrain". I checked on Google and it looks like many users were searching for blackrain today since they got iPhones or iPod Touches as Christmas gifts. A search for blackrain brought up a sponsored result to a site that is charging for the blackra1n software. Do not buy it, it is free and we have a guide on how to install it here.
To jailbreak your iPhone with blackra1n view the guide here, and to jailbreak your iPod touch view the guide here. Please spell out blackra1n to your friends if you ever mention it to them, otherwise they may end up paying for it and getting scammed!