Jailbreakme.com provides an immediate one-step jailbreak unlike more common jailbreaks, such as Blackra1n and redsn0w, that require plugging the device into another computer and running the Jail breaking software from the desktop. Jail breaking allows users to install software that is not approved by Apple on their iPod Touch, iPhone, and iPad; Jailbreakme automatically includes Cydia, a package management interface that serves as an alternative to the App Store.
Jail breaking your Device means you can use it with any other carrier or mess around of you device with installing applications you normally wouldn't download and even tweak it up to do whatever you want it to do. Its always a good idea to backup your information and have a few precautions when having your device free from its grounds because hackers and other malware are just waiting around the corner "just like desktops". The process takes about 2 min. and you have to access the website on your device instead of your desktop computer which means you don't need nothing more than your wifi and your iphone,ipad,ect device.
Jailbreak me provides a version chart
1.0
2.0
3.0
Some like my Iphone doesn't even support any version so I'm pritty screwed but...HEY I tried.