If it's a challenge to crank your car up and you hear a distinct clicking noise whilst doing so, there are generally two potential reasons for the trouble. It might be a dead or dying car battery, and it could also be the alternator. It's not unusual for the battery to be dead when the alternator is dead, but that's not always the case. If you do the following tests, you may be able to determine whether you've got alternator problems, battery problems or both.
The Battery Test
The battery test is dead simple, as long as you're able to get your car started. Whilst you might assume that you need a professional to check your battery, it's actually something that you can do at home in many cases. Open the bonnet and suspend it whilst you attempt to crank up your car. Once the motor is running, carefully take the negative cable away from your battery, leaving it disconnected. Your vehicle will respond by either continuing to run—an indicator that the battery likely caused the issue—or by stalling. If your vehicle stalls, odds are good that the problem results from a bad alternator.
The Headlamp Test
The headlamp test is another option that you can perform quite quickly and easily if you can start up your car. Whilst outdoors, simply crank up the car and switch on your headlamps. Have a friend stand in front of your car to observe whilst you depress the accelerator. Is there any change in the headlamps whilst you're depressing the accelerator? If your friend observes any change in headlamp brightness or any wavering in the headlamps, the odds are high that your alternator is the problem.
If You Can't Perform Your Own Tests
If you're unable to perform the tests above because your car won't crank up at all, it's best to take it in to be seen to by a professional. Whilst this might require a jump start from a friend—and a drive directly to the mechanic's shop with no stopping—it's usually the best course of action. Trying to continually drive a car with a bad alternator, a bad battery or both is going to inevitably end up being a more complicated and costly repair for you to deal with in the long term.
The best way to prevent long term issues is to repair or rebuild a faulty alternator before it fails completely. Contact your local mechanic who handles alternator rebuilds and repair if you're having battery problems, alternator problems, or both!