When you use your turn signal, your car has a corresponding light indicator on the dashboard to let you know the blinker is in fact on. This blinking notification also alerts you when there is a problem with one of the lights or a component of the flasher system that turns the bulbs on and off.
Every now and then, you will notice the light on your dashboard is blinking twice as fast as usual. This usually means one of the bulbs is blown and will need to be replaced. When you reach your destination, you can easily figure out if this is the case. Shut the engine off, but leave the car on so the electrical components are working. Turn on the offending blinker, hop out and visually inspect the front and rear turn signals. If one is out, replace it and the quick-blinker issue should resolve itself.
However, if both bulbs are not working, you could be looking at a problem with the flasher system. When the lights don't even turn on, check the fuse that corresponds to this component of your car. Replace it if it appears damaged. If this does not solve the problem, or if neither light is working, you may need to replace the flasher system. This is a complicated procedure involving intricate circuits and wiring, so you may want to have a professional address the issue.
When you are investigating your turn signals, you may want to check the hazard lights as well. These sometimes use the same relay as the turn signals but may have their own system depending on the make and model of your vehicle. Either way, if you're looking at one, you may as well ensure the other is working while you're at it.
It is important to address faulty lights as soon as possible, since they are used to communicate with other drivers. If your rear signal isn't working, someone driving behind you may not anticipate you are going to slow down to turn and you could wind up getting into a car accident. Replacing a light bulb only takes a few minutes and it can help you stay safe on the road and avoid costly damage.