Chances are you've already jailbroken your iDevice using Redsn0w. If you remember, that's a tethered jailbreak – meaning, you'll have to connect your iPhone to the computer (and start Redsn0w) every time you rebooted your iPhone.
Evasi0n jailbreak comes with an “untether” patch which helps you convert your tethered jailbreak into an untethered jailbreak. You can find the patch and apply it via Cydia.
How to Convert Your Tethered Jailbreak into Untethered Jailbreak for iOS 6.x
This short tutorial shows you how you can convert your tethered jailbreak into an untethered one.
Before we begin
Make sure you've backed up all data to iTunes/iCloud.
What you need
#1. Just the tethered iPhone/iDevice
#2. Data network (preferably Wifi)
Lets start how to convert the tethered jailbreak to untethered:
Step #1. Open Cydia(if Cydia begins to refresh the resources, let it do so. Once the refresh is complete follow the steps.)
Step #2. Tap on ‘Search' and type evasi0n 6.x untether in the search box.
Step #3. You'll find the respective package. Tap and open it.
Step #4. Download the package and let Cydia Install it.
Step #5. Once you've installed, test the package.
To do this, all you need to do is restart your iPhone. Press the power button till ‘slide to power off' shows up. Swipe the slider and then start the iPhone.
Once done, you'll see that the iPhone restarts normally, without getting stuck anywhere.
If in case it does get stuck somewhere along the boot, you should get your iPhone into DFU mode and restart via Redsn0w (using the tethered boot process). And then, apply the untether patch again just to make sure it gets installed correctly.
If you restored your iDevice and lost all jailbreak data, you can simply use Evasi0n jailbreak tool to jailbreak (untethered) your iPhone/iPad/iPod Touch.