Question

How does applying pressure (or coompression)help in the liquefaction of a gas ?

Answer 1

The physical state of matter can also be changed by changing the pressure. In other words, the physical state of matter can also be changed by increasing pressure or decreasing pressure. For example, gases can be changed into liquids by increasing the pressure (accompanied by lowering of temperature).
There is a lot of space between the particles of a gas. We can reduce the spaces between the particles by enclosing it in a cylinder and compressing it by pushing in the piston.