In terms of it's function, within an aspirator there is usually contained some form of fluid. This fluid is filtered through a narrow passing. The venturi effect indicates that as the tube becomes increasingly narrow, so the speed of the fluid will begin to accelerate, due to the reduction of fluid pressure at the most constricted part of the passage.
The most basic type of aspirator is the water aspirator. It is commonly found in a chemistry laboratories. This works by having water forced through a nozzle at high velocity. A vacuum is fitted at the smallest part of the nozzle. In addition to this, a tube is fitted at the side of the nozzle that draws up fluid. At this point, it interacts with the high velocity fluid and once they have mixed, they are together expelled from the nozzle exit.
This device is generally used to pump up any spills or to transfer water or fluids between different locations. In general, all of these types of aspirators function on the same basic principle. You can also find aspirators in the cosmetic field, such as perfume spray bottles that aspire the perfume and discharge it with high velocity air.
I hope this helps.