How to use this pressure cooker

I have a pressure cooker I just found and was wondering how to use it and what this attachment in it is for. I don’t understand what the twisting and the top green part which does not seem to do anything. This is the cooker https://ibb.co/cc1pzLQF https://ibb.co/fVrC8zGg https://ibb.co/HL1nMQ1q submitted by /u/Tuffbearr