Just i b ought sonata 2008 car and the tpms light is on and i donot know why

Its a tire pressure management warning your tires have a sensor advising of the tire pressure in them if one goes low it will set off the sensor and you get warning check the tire pressure one may be low it will auto reset when pressure has been corrected also check spare tire on some vehicles there is a sensor on it as well

Usually your RF (radio frequency) is messed up and sending invalid data to your computer. You will have to take your car to the dealer and have them reset it. Mine keeps coming on too. I keep asking them if there is a recall on this. Mine has come on 5-6 times. And if you live where it is cold, it will come on in the winter too. Don't worry about this one, when theh weather warms it will go off