After reading this topic Comparison between Open loop and Closed loop control systems, you will understand the theory and comparison.
Open loop control systems
It is a control system in which the control action independent of the output signal and depends only on its input signal, also the signal flows through the block is unidirectional. It is shown below,
Closed-loop control systems
It is a control system in which the control action dependents on both the output signal and the input signal. It is shown below,
As compared with the open-loop control system, an additional feedback feature in the closed-loop control system results in the relationship between the output and the input.
Comparison between Open loop and Closed loop control systems