why is the touch screen on my iphone 4s not working correctly?
Assuming that you haven't jailbroken your phone, the most likely culprit is a hardware part called the digitizer. If you live near an Apple Store, you can get get a free diagnosis of what is wrong by making an appointment at the Genius Bar. The repair will not be free if it is indeed a hardware problem, but then you will have a starting place. 

If you have a good up-to-date backup of your device, you can try restoring the operating system. Please be aware that the process of restoring can result in serious data loss (including text messages and photos) if you are not careful.