Make sure that the battery packs of the 2 vehicles are sufficiently near to connect with the jumper cables. Turn off the ignition on both auto-mobiles, put on the handbrakes and put them into neutral or park. Switch off both cars lights, if they are in a position that might be a danger to other auto-mobiles keep their hazard lights on. To jump-start an auto you need high quality jumper wires, it is wise to have a set of cables with you at all times.
The clamps must be clean and rust free as do the terminals on both auto-mobiles batteries. Start by clamping the red wire onto the + (positive) terminal on the battery of the broken down car then onto the positive terminal of the booster vehicle. Repeat with the black wire, but connecting to the - (negative) terminal on the booster vehicle and to an un-painted area within the engine bay on the lifeless auto or the engine block. Ensure that the cables aren't coming in contact with any bit of the engines which will move when the auto-mobiles are up and running.
Start the booster auto 1st, leave the engine to tick over for a couple of minutes, and then start the broken down car. Let both cars tick over for 1 or 2 minutes while hooked up. If the dead vehicle doesn't start after two or three attempts do not continue to keep trying. To do so, would strain the booster vehicle's battery and may ruin one or both of the vehicles. When you detach the cables, take pains not to let the wires touch any moving part of the engine or touch one another.
Do not turn off the broken down car's engine; you will need to drive several miles to allow the battery to recharge. Not doing so will mean that you cannot re-start the auto-mobile without jumping it again.