Jailbreaking -- the process that enables you to install unauthorized-by-Apple third-party apps and additional features on your iPhone, iPod touch, and iPad -- has been in a largely dormant state since the release of iOS 6. In that version of the mobile operating system, Apple closed many of the avenues jailbreakers had once used to crack it open.
Tethered jailbreaks had been developed for iOS 6, but they were clumsy. Such jailbreaks require you to attach your iOS device to your computer (thus, the tether) and run an application to jailbreak it. If you later power off the device and then restart it, the jailbreak is wiped out, and you must repeat the entire tether-and-jailbreak process.
What those who desired to jailbreak iOS 6 wanted was an untethered method -- one in which the hack would remain in effect even after the device was powered down and then powered up again.
That untethered jailbreak recently arrived in the form of evasi0n, a jailbreak designed for devices running iOS 6.0 through 6.1. Like jailbreaks before it, evasi0n doesn't unlock an iPhone (which would allow you to use the device with multiple carriers -- and which has also been deemed by the U.S. Librarian of Congress to be illegal). Rather, it allows you to install third-party apps not approved by Apple via the Cydia store.
Before I explain how it's done, you should be aware of Apple's advice on the subject of jailbreaking. In this tech note Apple suggests that doing that to your iOS device may lead to security vulnerabilities, instability, shortened battery life, unreliable voice and data, disruption of voice and data, disruption of services, inability to apply future software updates; it may result in Apple denying service for your device.
That said, I've been jailbreaking iOS devices for years and have not encountered these issues. But once I've jailbroken such a device, I understand that I should expect no help from Apple if it causes me trouble in the future. With choice comes responsibility.
You should also be aware that the Librarian of Congress has deemed that, while it's legal to jailbreak a phone, doing the same thing to a tablet is a different matter. For reasons best known to those who create such arbitrary distinctions, tablets are to be treated differently. So while the operation I describe works with all iOS devices, you risk incurring the wrath of the law if you undertake to jailbreak an iPad.
Breaking it down
With the warnings out of the way, let's get started.
To begin, back up your device. You do this by plugging it into your computer, launching iTunes, and choosing File > Devices > Back Up. This helps ensure that any data you have on your device can be later restored.
Now download a copy of evasi0n from one of the mirror sites listed on the evasi0n site (it's a download of just over 10MB). Double-click the .dmg file to decompress it and an evasi0n window will appear on your desktop. Drag the evasi0n application out of the window to the desktop and launch it.