I have provided a diagram above to aid in this answer. The diffusion pump is a very common mechanism for creating a high vacuum. Generally, the pump contains three cone-shaped pressure jets stacked vertically. There is pump oil at the bottom that is heated until it reaches a gaseous state. In the gaseous state, the oil will travel upward and exit through pressure jets in a downward direction. As the vapor travels towards the walls, it will trap air molecules that enter the pump through diffusion. With the cooling coils on the walls, the vapor will immediately condense, releasing the trapped air molecule at a lower position. The oil will travel back to the heater where the process will continue, and the air molecule will be removed via the backing pump and thus creating the high vacuum.