A cooling tower is an installation in which heat is withdrawn from water. In industry, including the chemical industry, this water is used as a coolant for all kinds of processes.
Industrial chemical processes often require cooling, for which water is used, just like with modern cars (some older models like Volkswagen Kever are cooled by air).
Analogous with a car, the water in a chemical installation is pumped from the process to the cooling tower and back. The water-cooling of a car takes place in the radiator: in the chemical industry a cooling tower is used.
A cooling tower is not a chimney from which smoke escapes. A small part of the cooled water evaporates and is sometimes visible in the form of a plume or mist above the cooling tower. This plume has the same composition as an ordinary cloud.