A matrix keyboard has switches that connect 'row' wires to 'column' wires. The processor energizes one 'row' at a time and if one or more of the 'column' wires becomes energized it can conclude that the switches connecting the energized row to those columns have been closed.
A 'touchpad' is usually an analog device that produces voltage signals that indicate where on the surface the pad is being pressed. A resistive touchpad usually has four connections: X-max, X-min, Y-max, Y-min. The processor energizes them in pairs and measures the voltage on the other connections to determine where the pressure is.