AWD question

I have an 04 Mountaineer with AWD and even with reading my owners manual and some research on line, I'm not sure exactly when I am using all wheel drive. Do the front wheels only pull in if the back wheels slip? Is it only AWD at slow speeds then the front wheels drop out? I use my Mountaineer to launch and retrieve my boat on a gravel ramp and it has done extremely well while at the same time numerous 2WD trucks have got stuck so I'm wondering if I am using AWD. Anyone know? Thanks.

The AWD system uses a viscous coupling unit (VCU) in place of a standard transfer case as used in the 4WD systems. The VCU is providing torque to all 4 wheels all the time, but the VCU allows the front and rear shafts to turn at slightly different rates, preventing the binding that would be experienced if it was a 4WD system.

-Rod