The breakout board (BOB) plugs into the parallel port and provides labeled terminals to connect wires to. I like optoisolated BOBs, with features like LEDS to observe signal state, pull-up/down input resistors, one or two output relays, lots of ground connections, and good signal conditioning circuitry to guard against noise. I used C11 Multifunction CNC Breakout Board | Automation Technology Inc for $129.00 Port pins are TTL devices with 5 volt signals which are either off or on. You cannot connect other voltages or analog signals to such digital port pins. Input pins should never be left open, they should be tied to positive or ground with a resistor, or else they can float and pick up false signals.