Matt gives an OK description, but it is missing some important points, such as attachment order, so please consider these instructions:
1) Park the good car so that its battery is as close as possible to the dead car’s battery, and turn off the ignition.
2) Expose the battery terminals and attach one end of one cable to the + terminal of the good car.
3) Attach the other end of that cable to the + terminal of the dead car.
4) Attach one end of the other cable to the—terminal of the good car.
5) Attach the last remaining clamp to exposed metal of the car somewhere other than the dead battery. This is to avoid potential explosions from sparks and leaking batteries. Anyway, I remember the full order as “good plus, bad plus, good minus, bad car.”
6) Start the good car, leave it in park, and gently feed some gas to rev the engine for a half a minute or so.
7) Have the other person start their car. If it doesn’t start, you may need to feed fuel to the good car’s engine for several minutes before trying again.
8) When the dead car starts, remove the cables in the reverse order that you clamped them (bad car, good minus, bad plus, good plus).
9) Don’t turn off the bad car until you are in a place where it’s OK for it to die again.
(Edit: Gave the list bullets to be easier to read.)
Matt gives an OK description, but it is missing some important points, such as attachment order, so please consider these instructions:
1) Park the good car so that its battery is as close as possible to the dead car’s battery, and turn off the ignition.
2) Expose the battery terminals and attach one end of one cable to the + terminal of the good car.
3) Attach the other end of that cable to the + terminal of the dead car.
4) Attach one end of the other cable to the—terminal of the good car.
5) Attach the last remaining clamp to exposed metal of the car somewhere other than the dead battery. This is to avoid potential explosions from sparks and leaking batteries. Anyway, I remember the full order as “good plus, bad plus, good minus, bad car.”
6) Start the good car, leave it in park, and gently feed some gas to rev the engine for a half a minute or so.
7) Have the other person start their car. If it doesn’t start, you may need to feed fuel to the good car’s engine for several minutes before trying again.
8) When the dead car starts, remove the cables in the reverse order that you clamped them (bad car, good minus, bad plus, good plus).
9) Don’t turn off the bad car until you are in a place where it’s OK for it to die again.
(Edit: Gave the list bullets to be easier to read.)
Step (9) here is the one that I didn’t know when I first jump-started a car. The others were in the instructions that came with the cables.