The alternator in your car is essentially a miniature generator that produces the power needed to keep all the electrical bits on your car up and running. The alternator begins producing power as soon as your car is started, and will continue to do so until the car turns off--providing the alternator is working correctly, of course. This power is transferred directly into your car's battery, which then funnels the power into any of the many electrical systems in your car that may need it.
Ensure that your battery cables are properly connected to the battery.
Start your car.
Let the car run for around half an hour. Most cars idle fast enough that the alternator will be able to charge a battery while sitting at idle.
Turn off your engine and test your electrical systems. If they work properly, your battery has been charged. If they do not work, or are sporadic, turn your car back on and drive around for another half hour. After the drive, your car's battery should be sufficiently charged.
