Your tire pressure light is illuminated because your car’s onboard computer has detected that the air pressure inside one or more of your tires is low. This can be a sign that you need to buy new tires, but it might also be an indication that there is a leak in your tire and you should have them inspected as soon as possible. If the light comes on while driving, pull over as soon as it is safe to do so and check all four of your tires for visible leaks or damaged rims. Check for any objects lodged in between the treads of the tire by rolling each wheel back and forth gently.
If you find nothing, add air to your tires if possible, or have a repair shop add some air using a tire gauge. Check the pressure on each tire again in several days and note whether it has changed significantly. If it hasn’t, continue to monitor the tire’s pressure weekly until it does change, which indicates it needs to be re-inflated. If you do not have a tire gage, stop by your local auto parts store and buy one for about $10.