Touchscreens are usually one of two forms;
Resistive touchscreens are passive and respond to pressure on the screen. They allow a high level of precision, useful in emulating a pointer (as is common in tablet computers) but may require calibration. Because of the high resolution, a stylus or fingernail is often used. Stylus-oriented systems are less suited to multi-touch.
Capacitive touchscreens tend to be less accurate, but more responsive than resistive devices. Because they require a conductive material, such as a finger tip, for input, they are not common among stylus-oriented devices, but are prominent on consumer devices. Finger-driven capacitive screens do not currently support pressure input.