What causes gas pressure?
Pressure is caused by the collisions between the atoms of gas and walls of the container as those atoms travel in the confined space.
There are three ways to increase the pressure:
Add more gas. More molecules mean more collisions. Like blowing more air into a balloon, the walls of the balloon get tighter.
Decrease the volume. Less space means less room for the atoms to move in and this will lead to more collisions and more pressure.
Increase the temperature. More energy means the atoms will move faster and will collide more often, more collisions more pressure.
I hope this was helpful.