Thank you for the opportunity to help you with your question!
All particles of a substance contain kinetic energy hence, they are continuously moving. Gases have high kinetic energy which makes it resist the attractive forces holding the particles together. The overall forces of the gas is responsible for all these collisions divided by the area of the walls of the container it is confined in.
For a fixed mass of gas, at a constant temperature, the product (pressure multiplied by the volume) is a constant.
Pressure × volume =constant
p x V = constant
Please let me know if you need any clarification. I'm always happy to answer your questions.