This feature-length film presented by Vince Cobley, who literally wrote the book on off-road driving, does an excellent job explaining how differentials work, what "four-wheel-drive" really means, and how to get your truck through just about anything. In delightfully classy English fashion.
These clips have been around for awhile, but nothing's changed about the principles Cobley's discussing. And after all, Series Land Rovers only get lovelier.
Part I: What 4WD really means, avoiding transmission windup, the importance of articulating suspension, why breakover-angle matters, water crossing, up & down hills, securing cargo, and pretty much everything else you need to know about off-road driving:
Part II: Land Rovers flexing and bogging around off-road courses, owners singing their praises, good times at English off-road meets: