If the plow is bouncing off the ground, it isn't set up correctly. If this is an A-C plow, I would suggest you get a manual for it. This should tell/show you how to properly set it up so it works as it should.
Check the hydraulic fluid at the transmission fill plug. Oil should just run out when the transmission/differential/pump is full. The transmission/differential/pump holds 7 quarts. The filler plug should be a square headed plug on the side of the transmission about 16" behind the clutch pedal at the junction of the transmission case and the left hand axle. The original manuals specified SAE 20W non-detergent oil. This is important to prevent the foaming that detergent oil will cause. A good grade of hydraulic oil such as Agco 821 (I think that is the number) or I-H Hy-tran can be used, but in systems that are not in near 100% condition, they may not work as well. I can find 20W non-detergent oil and Traveller hydraulic fluid (an acceptable substitute for the Agco or I-H fluid) at my local Tractor Supply Co. (TSC) store.