It got really hot inside the cooker and the air expanded. A lot of the air was forced out under the lid. When you take it off the heat it cools down and the air inside contracts as it cools and it forms a partial vacuum that holds the lid on.

Because when you heat the water inside a cooker the heat energy transfer to the water and it starts boiling when the water start boiling it generates steam this steam has high pressure and the high-pressure exerts on the walls of the container and also on the lid because of this pressure and heat we can't open the lid off the steam cooker

Because there is Steam Hold by cooker for cooking Until unless entire steam either condensate or released pressure cooker can't be open or else it may burnt your body parts

Place the food to be cooked inside the pressure cooker, with a small amount of water.Preferably soak items such as lentils, rice etc. as it reduces cooking time and saves fuel

There is steam under pressure.So allow to cool it,reduce pressure then u can take out lid.

Cause it's a tight fit. The engineering to make these isn't so great.