Set parking brake.
Push clutch in all the way.
Put gearshift in neutral.
If car has fuel injection, just turn the key and car should start.
If car has carburetor, you may have to pump the gas 1x before you start it.
hope this helps.

Some manual transmission cars require the clutch be depressed even if
you are in neutral.

If you mean "when the battery is dead" then

put the transmission in 2nd or 3rd gear
turn on the ignition,
get the car rolling at a good speed ( a few mph; usually takes one
person to push and another to operate depending on the doors).
let out the clutch and it should start.

might take a couple tries.

May damage the catalytic converter if too much unburned fuel gets to it.