This chip is like a rotary switch - it internally routes the common pin (COM in the schematic, SIG on the board) to one of 16 channel pins (CHANxx). It works with both digital and analog signals (the voltage can't be higher than VCC), and the connections function in either direction.
A method for controlling the motor, lights, LED, DC motors, micro-pumps, solenoid valves, etc., very convenient.