You get into your car as usual, put the key in and turn on the ignition. Nothing. The car doesn't start. The reason is probably that your car battery has died out. It cannot supply an electric current, that is large enough to start ignition. One straightforward way out of this, is to get a charger connected to a power supply, to restore charge levels.
The other way, in case you do not have a charger or a power supply around, is to jump start it. It is quite a simple technique to get just about enough charge, to trigger ignition and get to a place where you can get the battery charged properly.
A word of caution. There is a very minute possibility of an explosion, caused by inflammation of hydrogen gas, created from the discharge of the battery. However, a proper technique of connecting jumper cables can avoid this problem.
Anyway, for an explosion to occur, the hydrogen gas will have to be quite dense and the car battery will have to be sitting dead for quite some time. Just follow the proper technique that is recommend here and you don't need to worry about this problem. The trick is to avoid sparking when jump starting. Wear safety glasses and gloves, during the procedure.
To pull off the procedure, you must have a pair of jumper cables with you. This technique is impossible without you having access to another working car, with a soundly charged battery. Make sure that the booster car's battery has the same voltage rating, as that of the dead one. Here's the procedure.
Park Booster Vehicle and Switch off Electrical Accessories in Both Cars
First thing to do is to get the working car and park it near your car. They should be close enough for the jumper cable from one battery, to reach the other, without touching. Shut down the working car and put both of them in neutral gear. Next, turn off all the accessories in the boosting vehicle, that consume electricity. This includes the radio, air conditioner, the windshield vipers, etc.
Connect Booster Cable to Positive Terminal of Both Car Batteries
Open the hoods of both the cars and get a good clean pair of jumper cables. Identify the positive and negative terminals on both the batteries, by the '+' or '-' sign. In case, the terminals are rusted, you may have to scrape off the rust, before you go on to connect the jumper cables. The first step is to connect one positive (red) end of the jumper cable to the positive terminal of the dead vehicle's jumper cable.
Make sure that the clamp of the cable is biting into the battery terminal and connected securely. The other end of the red jumper cable should be connected to the positive terminal of the booster vehicle's battery.
Connect Negative Terminals and Ground the Connection
Next step is to connect the black (negative) jumper cable, to the negative of the booster vehicle's battery. Then, connect the other end of the negative jumper cable, to a ground position. This ground position is any part of shiny metal on the car chassis. Make sure that this grounding point is far away from the dead car battery. This reduces the danger of an explosion, while providing a solid ground for your charge transfer process. Make sure that the ground connection is firm.
Turn on the Booster Vehicle and Start Charging
Before you go ahead, make sure that the cables are not coming in the way of any moving parts, under the hood, in both cars. Now, start the booster vehicle and keep it in idle mode for a while, till the charge transfer happens. In case, the dead battery has been in that state, for a long time, this will take some time. After some time, try starting the dead car.
Chances are that if there aren't any other problems, the car will start easily. Once it has started working, remove the cables off the batteries, in exactly the reverse order of connection. Close the hood of both cars, switch off the booster car and keep the car with the jumped battery running. Drive it to a location where you can get the battery charged fully, using a charger.
This simple technique can certainly come in handy when you are stuck and stranded due to a dead battery.