The .1″ headers are mounted on the bottom of the PCB for simple insertion into a breadboard. Pins labeled VCC and GND plug directly into the power lines. The lone pair of pins have no electrical connection but help support the PCB.
There are two pins available within the barrel jack footprint. Any stripped +/- DC supply can be connected instead of the barrel connector. Board has both an On/Off switch and a voltage select switch (3.3V/5V).