The liquid in the jar is at atmospheric pressure (there's a vent hole connecting it to the atmosphere). A fast jet of air flowing right over the end of the pickup tube sucks the liquid up the tube and into the air stream. How exactly does this fast stream of air creates suction? It's released in the atmosphere, so shouldn't it also be at atmospheric pressure?
this is called an aspirator pump. By blowing a jet of air across the top of the dip tube, a slight negative pressure is developed there and the air in the end of the dip tube is thus urged to join in the flow. This draws fluid up the tube which then gets dispersed into the jet.