Here’s how to jailbreak iOS 8.1.2 on Windows:

Step 1: First up, download TaiG v1.2.0 or over for Windows.

Step 2: Connect your iPhone, iPad or iPod touch to your computer via USB.

Step 3: Start TaiG. Uncheck the 3K Assitant option and hit the green Start button.

Step 4: TaiG will now begin to jailbreak your device. During the jailbreak process, do not disconnect your iPhone, iPad or iPod touch. Once it is complete, your device will restart and you will have latest version of Cydia installed on the main home screen.