There are 3 things that work in concert:
The descent rate dial (the one in the Messick's video). Whenever you hook something up in the middle or rear of your tractor, first thing: close off the descent rate valve, then verify it later on before pushing the hydraulic leaver forward to drop the implement so it doesn't slam to the ground (that sucks).
The "wheel" or "roller" or "anti-scalp" height on the mower deck: Set those rollers to the correct height so your mower blades don't dig into a hill or shave the tops off rocks or patio pavers that stick up (at least until you get the hang of mowing). The correct setting is in the Owner's Manual.
The Mid-Mount Mower cutting height dial, which can only be turned one direction--set that to the same setting as the anti-scalp rollers.
I'd also mention: The PTO driveshaft should "snap" into the locked position on the PTO Output Shaft. Once the driveshaft is on give it a good pull to make sure it's actually locked on and doesn't pull off without releasing the locking collar first.
Engage the blades at idle, slowly, with the deck slightly raised for the purpose of minimizing stress on the clutch (the clutch-at least on my tractor-is really, really expensive), then slowly increase the engine speed to the correct RPM.