Cars with manual (stick shift) transmissions can be started even when the battery or the starter motor isn't working. Here's how you do it.
Make sure that the problem is either the battery or the starter: If the engine cranks ("rrr-rrr-rrr") when you turn the key, then the problem isn't the starter or the battery.
Plan to have at least one person sitting in the driver's seat and one person pushing. Mid-size and large cars require two or three people to push, depending on the strength of the people and whether or not the car is parked on an incline.
Turn off all accessories (radio, wipers, lamps).
Turn the key to the "on" position.
Depress the clutch pedal with your foot.
Put the transmission in first or second gear.
Release the hand brake and the foot brake.
Note that the people pushing need to get the car rolling as fast as they can. This works best down a hill or an incline.
Release the clutch pedal while giving the engine a little gas with the gas pedal once the car is moving about as fast as you can run. The engine should start.
Cars can be push-started going backwards, too! Just put the transmission in reverse instead of first or second and push the car backwards. A car with a completely dead battery often cannot be push-started.
One person can push-start a car that is parked on a hill, but this can be very unsafe as you must jump in the car after getting it rolling, and there is a chance you may lose control of the car. Certain manufacturers of specific models do not recommend starting your car this way. Check your owner's manual for warnings.