Term 3 has a pretty good understanding. 4L and 4H is a gear change in the transfer case. Stick it in low and you'll see. The hubs auto lock but as with any open/limited slip differential the least traction is the easiest to spin and it will. Locking them in locks them both, but this is harder on your components because nothing gives. Auto-lock is fine for 90% of the situations manual lock is your maximum traction but harder on your stuff for driving distances.