You need the Owner's Manual.
Do a web search for King Kutter or contact your seller (perhaps Tractor Supply?)--you said it was new--and obtain the Owner's Manual for your model.
Rotary cutters, shredders, bush hogs, brush hogs, are safe if used correctly and if not used correctly can create in you a bit of heartburn.
You need to know about the shear pins (bolts you were furnished), lubrication, grease zerks on U-joints, gear box oil, blade removal and sharpening, drive-line attachment to tractor, how to adjust the unit for different conditions, replacement part numbers, your stump-jumper or bar-mount, blade bolts----everything.
When using the cutter don't let anybody else ride on the tractor. Ever. Every year around here a kid falls off the fender and gets chopped up before Pop ever knows what's happened.
Depending on what you're cutting sooner or later you'll bend or break a blade. Think ahead about this possibility and be prepared how to react quickly.
You may need a 'special' wrench to remove the blades---standard size (mine are 1-3/8-in), think of a socket-on-a-stick (with 15-in Crescent and cheater) or use or obtain a 3/4-drive breaker bar with socket and extension.
Sharpen blades using a 4-1/2-in hand grinder or bench grinder.
Previous poster mentioned circlip to retain driveline when pin on gearbox shears. Not so in all cases. One of mine doesn't and first time it sheared it popped off the gearbox input shaft and started flopping around on the deck wildly at 540-rpms. Spooky.
Check this aspect and if you need create a restraint harness out of light strap or chain or cable run through heavy hose situated near the gearbox between the lift frame verticals and looped loosely around the driveline. Same as if a blade breaks, get out of the PTO FAST, clean the seat, repair, and go on about your business.
Please advise your experiences and progress so we may all learn.