The legal answer varies by jurisdiction; in most North American states and provinces the legal requirement is along the lines of requiring headlamps one half hour after sunset until one half hour before sunrise, and in conditions of reduced visibility such as inclement weather. Some states and provinces are adopting laws requiring that the headlamps be turned on whenever the windshield wipers are operating (except for brief operation to clear away a splash or clean the windshield).
Practically, you should use the headlamps whenever they are necessary or helpful to your seeing or being seen. Always only ever use low beams, never high beams, in bad weather or if there is any driver on the road in front of you in either direction. And remember that a vehicle's daytime running lights, even if they are implemented by operating the headlamps in one or another manner, are not an adequate substitute for the full/real headlamps.
It depends upon driving condition (not time)
You should turn on your car's headlights at dusk and when it is raining. It is also a general practice to turn your headlights on when in a funeral procession. You should check with your local motor vehicle bureau, since regulations may be different in the area you will be driving.
Wipers
You should flick the headlight switch after you turn the car on.
the low beams should turn on when the motorcycle is turned on
Night time.
when it is raining or at night. Also generally when it is dark.
All the time
turn on your headlights
turn on your headlights
There are a couple of different times when you'd turn off your headlights. You'd turn off your headlights when the car is off for example.
The headlights should turn on and off automatically depending on which setting you have your switch set at. The switch is located on the turn signal lever. I always leave mine on auto.