understanding 4wd

[tracengrant]

in the face of looking really stupid could someone please tell me how to use the diff lock/unlock and hi/low wot are each of these used for and when would u use them i was sliding in slushy snow so stuck into diff lock on my landrover discovery and we went quite well but dont wanna kn acker my motor. Do u have to be at a standstill to engage diff lock etc sorry for all the questions but can someone help an idiotic girly lol

[Jantiz]

Is it a disco 3 or an earlier model?