When Clutch should be engaged and disengaged of an automobile?

Axle:

There are two types of Axle:

1.     Line Axle:  Line axle route itself.

2.     Dead axle: It is only route wheel.

Clutch:

It is a mechanism which enable the rotary motion of one shaft to be transmitted other shaft which are coincident with the first.

Why Clutch should be engaged and disengaged?

Clutch Engaged: 

When vehicle is running clutch must be running.

Clutch Disengaged:

i.                   When Starting the Engine.

ii.                 When shifting the gear.

iii.              When stopping the gear.

iv.              When Idling the engine.