in terms of what the axle does or does not do, thanks

gear reduction in low

It pretty simple actually. l think the explorer has a 4-speed automatic, which in a normal car would be connected straight to wheels via differential & axles. In ur ford there is almost like a second transmission that changes the FINAL gear u r in. It is like gears on a bicycle. You have 1-2-3 on one side & 1-2-3-4-5-6 on the other. If u r in 1 & 1 u will be going slow but pedaling will be very easy, but if u r in 3 & 6 pedaling will be hard but u will be going very fast.

4WD has a transfer case, which sends power to just rear wheels or all 4 wheels, it has 2 different drive ratio is made in it, in 4WD low ratio is lowered to give engine more power to pull, though it wo not go fast, regular 4WD is like 2WD, but with the 4 wheels pulling

The functions r the same as far as what the axles do. In 4WD low ur top speed is going to be probably less than 40 MPH. Usually better for going through snow, sand or mud but can also get u stuck faster if u do not know how to use the speed & traction together for the conditions. 4WD high is usually better for icy driving conditions on solid roads while 4WD low would be better for rough sloppy terrain. Whichever one u choose to use remember that neither one will stop u any faster than a 2WD when u r on ice & slippery surfaces, it only helps u go faster through the soup.

4wd high will allow you to drive on dry payment and normally can go up to 45mph with the front axles moving. 4wd low will not allow you to drive faster then 10mph, this control the speed and traction of the vehicle.

High or low 4wd has nothing to do with the axles. It only affects the transmission gear ratios.