Reducing temperature and applying high pressure on a gas can lead to:
Applying pressure means forcing the atoms of matter towards each other (reducing the free space between the particles). Thus, the application of pressure reduces the inter-atomic distance. As a result, the application of large pressure changes the gas into liquid first and then into a solid.
Reducing the temperature reduces the kinetic energy of the matter; thus, atoms of the particle will not move in random motion and will convert into liquid. Hence, applying high pressure and reducing temperature leads to liquefaction of gasses.