Process control can essentially be considered a branch of engineering that deals with integrating the various engineering elements like machine architecture, its mechanism and algorithm required to output some specific process. This is usually used where the repetition of the same process is required. It is mainly used for in industries where mass production is required.
Process control can be manual or automatic. One example of process control is our daily life is the Air Conditioner (Automatic Temperature Controller). It is made up with the combination of various elements with mechanisms fixed to each other in a given algorithmic architecture.
The major elements used for the Automatic Temperature Controller are the temperature transmitter, A signal line, and three Controllers serving three different purposes of controlling the temperature of hot water, adjusting the correcting unit and providing the alarm signal. Other minor elements are also used in ATC that serve other minor purposes in the algorithm of the architecture.
This was one simple everyday example of process control.