To use PiP on your iPhone 12, first make sure that you have the latest version of iOS installed. Then, open the app that you want to use PiP with and start playing a video. Once the video is playing, tap the PiP icon in the bottom right corner. The video will then shrink down and move to the corner of your screen. You can move the PiP window around by dragging it, and you can adjust its size by pinching or expanding it. To exit PiP mode, tap the PiP icon again or press the Home button.