There is a small yellow window behind sq20. You can see it when you open it. Just put it in, it's S, and then count down to 10-0. You can't open the lid when it's installed. The consequences of opening the lid are either very serious or you will waste one.
SQ20 is a Polaroid camera owned by Fuji, and its full name is Fuji instaxSQUARESQ20.