This article written in 2010 is an overview of the differences between capacitive and resistive touchscreens.
Here's another video about how touchscreens work.
Want to learn more about screens on your mobile devices, computer monitors, and televisions? Start here: Watching a movie at home isn’t quite the same experience as seeing it at a movie theater -- but why? Learn how changes in aspect ratio affect every film, and why your television might not be delivering the whole picture.
Perhaps you should brush up on your electric vocabulary before you delve into the inner workings of a touchscreen. We all know the words around electricity -- “charge,” “positive,” “battery” and more. But where do they come from and what do they really mean? Let the history of these words illuminate the physics of electric phenomena.