First off pushing the hand clutch away from you is similar to stepping on the foot clutch in that it releases the power from the tranny. Pulling the hand clutch towards you is like letting up on the foot clutch in that it puts power to the tranny. With both clutchs pushed away from you (foot down, hand away) you engage the brushhog by pulling the PTO knob towards you. With your right foot also on the brakes put the tranny in gear (I use 2nd for most hog work, 1st if its really thick). Letting up slowly on the foot clutch should spin up the hog while the tractor stays put. Slowly release the brakes and gently pull the hand clutch towards you to put power to the tranny.
Careful note here. In 1st gear if you pull the clutch back too fast you can pop a wheely real easy. Also when the tractor first moves forward if your hand isn't braced against the right fender you can inadvertently yank the hand clutch towards you and also pop a wheely. In 2nd gear the hand clutch works much smoother. I've been told you can slip it as much as you want since its a wet clutch so 2nd is the gear for me.
Also note: With the hand clutch pushed away from you and foot off the engine clutch, the tractor should come to a stop especially when you hit the brakes while still allowing the PTO to power the hog. If it doesn't, your hand clutch is stuck and isn't releasing the power to the tranny like it should.