Very basically, you have 3 differentials, one on each axle, and one on the output from the gearbox, in normal *open* drive the vehicle will stop if you loose traction on 1 wheel although they are very capable.
You have high range and low range, you normally travel on roads in high range (small gearknob to the right & back)
For "Off-road" you will use low range mostly, (small gearknob to the right but forwards)
*To change from high to low, or low to high, first reduce your speed to walking pace ie 4mph or less whilst driving in a straight ahead manner, take the main gearstick out of drive and into neutral and let the clutch up, now move the small gearknob into the position you want, low or high, then you will select a gear with the main gearstick as normal.
You also have *Difflock* this is available in both high or low range, this works on the centre diff that's attached to the gearbox.
Everything about changing the small gearknob into the correct range is the same as before, but this time take it out of drive and into it's neutral position, then move it across to the left and select the range you want. The move across to the left will put it into difflock. This *locks up* the centre diff, and 50% of the drive power goes to each axle.
When in difflock, you should have a light on the dash that looks like a H with wheels on.
You need to be in the correct range, with difflock if needed, and the correct gear BEFORE you tackle any obstacle.
You would only use difflock if there is a chance that you might loose traction, and get out of it as soon as it's not required, leaving it in on tarmac etc can damage your transmission.
You can still loose traction with it in difflock if 1 wheel on each axle looses grip.
As a very basic guide, for normal driving and going up hills, use 3rd low.
For down hill gradients, use 1st low.
If you feel that you might loose traction, either due to mud, ice, snow, or rocky steps, engage low with difflock.
DO NOT try to change gear either part way up, or going down a steep hill.
(This is as you requested, BASIC instructions on how to drive using the various ranges, you will adapt more as you get more experienced)