working principle of hydrolic cylinder

The oil start to flow through the input which existing at the left side and when the oil increase at the left side the pressure will increase at this side , result of this pressure the piston ( plunger at this picture ) start to move to the other side and this movement will rise up the load which we want to rise it up , we now get what we want , but for repeat this process we must down the piston as it was at the starting state , to do this the oil start to flow through the right side and the pressure will increase at this side which result to push the piston to left and this movement will return the piston to the starting state which allow to us to use it again to rise another load .