The fascinating world of power hydraulics!!
A short note on What is Hydraulics.
Hydraulics is basically a branch of mechanical engineering that uses a confined fluid to transmit power taking advantage of its physical properties, such as its incompressibility, his ability to "flow" in containers such as pipes and others. The source of power to be transmitted can be obtained from electric motors, gasoline engines etc.
The hydraulic system receives the power to transmit using an element called "hydraulic pump" that is responsible for sending a fluid from a reservoir into the hydraulic system output to do the work to be performed by the element called "actuator" which can be linear (hydraulic cylinder) or rotating (hydraulic motor). This fluid sent by the pump will generate movement in the actuator with a speed that will depend on the amount of fluid sent by the pump per unit of time (flow), and the load that the actuator will have to overcome will generate hydraulic pressure to be injected by the pump into the hydraulic system. Between the pump and the actuators must other hydraulic elements called "valves" with very specific functions. There are pressure control valves, flow control valves and directional control valves. Depending on the application and the nature of the work to perform there would be more or less valves.
I hope this quick and short explanation can help to begin to understand how hydraulics works.