IR Break Beam Sensor consist of a IR Transmitter and a Receiver. They work by having an emitter side that sends out a beam of human-invisible IR light, then a receiver across the way which is sensitive to that same light. When something passes between the two, and its not transparent to IR, then the 'beam is broken' and the receiver will let you know.
The receiver is NPN open collector output which means that you do need a pull up resistor if you want to read a digital signal off the signal wire. Most microcontrollers have the ability to turn on a built in pull up resistor. If you do not, connect a 1K resistor between the Yellow/White wire of the receiver and the red wire. If you want to control a relay or LED or whatever, it can sink up to 70mA to ground