When people notice that an unexpected light comes eliminates on their dashboard, they usually don't know what it means.  I always suggest they look at their Car User's Manual.  All owners should reference this book for more knowledge of their cars, i.e. maintenance intervals, all dashboard indicators, dashboard lights, liquid capacities, and tire pressure.

First off, tire pressure should be checked and set when the tires are cold. 

To determine what your tire pressure should be at, look for a factory sticker on your driver side door or drive side door jam.  It should look something like this:

This sticker tells you what pressures your front and rear tires should be inflated to.  Please read carefully since sometimes the front inflation setting is different than the rear setting.

Now that you have the information that you need, ensure you had a good quality tire gauge.  Inflate all FIVE tires to the proper setting.  After you inflate all FIVE tires to the proper setting, the Tire Pressure Light should turn off.

For more information on how tire inflation affects your tire life, Read On

I found this article to be very good for more information on Tire Pressure Sensors: Read On