I'll add a bit to what ritcheyvs mentioned, You have a forward and reverse lever on the left hand side next to the steering column, You use the clutch to select frwd or rev with whatever gear you have selected.
I do shift through the gears for various things, If I am getting ready to go down the road I will usually start out in high range first gear, When I have some momentum I shift to second then third etc.....When I come to a stop I push the clutch in and apply the brakes till stopped, I don't down shift...
Good luck, The DK is a awesome tractor...