Yangtze is the first semi-untethered jailbreak for iOS 12 beta 2, allowing users to install tweaks and themes from the Yangtze Store. It requires backing up the iPhone, turning off features like Find My iPhone, and using Cydia Impactor to install the Yangtze IPA file while the device is in Airplane Mode. The jailbreak process involves launching the Yangtze app and tapping the Jailbreak button to complete installation of the Yangtze Store on iOS 12 beta 2 devices.