iBooty is a separate piece of software that is required to boot your iPhone, iPod or iPad into Tethered Jailbroken State. Firstly your iOS device is jailbroken with sn0wbreeze and then iBooty is used to make the device boot.
Only iPhone 3GS (Old Bootrom) users are not required to use iBooty as they can jailbreak their iPhone on iOS 4.3 untethered using Sn0wbreeze 2.3. If you are unsure about your device, use this tool to know your sate of Bootrom in iPhone 3GS with this tool.
A tethered jailbreak requires that the device be connected to a computer each time it needs to be booted into a jailbroken state. An untethered jailbreak allows the device to be powered off, powered up, and rebooted without having to use the assistance of a Macintosh or PC.
If you are using iBooty, it means the jailbreak is tethered. Using iBooty is easy, the only thing you need to care is pressing of buttons. Here are the steps.
1. Start iBooty and connect your device to computer or laptop via USB.
2. Now, select the device.
3. Press Home+Power button simultaneously for 10 seconds.
4. After 10 seconds, release the Power button but keep pressing the Home button until iBooty detects your device in DFU mode.
5. It will patch your iDevice with Limera1n and your device will boot automatically. Wait for sometime for device to start.
If something goes wrong with timing of pressing those buttons, than start all over again.
When you create iOS 4.3 custom with Sn0wbreeze, iBooty is automatically placed on your desktop with necessary files.
Current Version of SnowBreeze can be downloaded from here.
You can check this page for direct download links of iOS Software updates from Apple.