These pins are referenced in the Arduino IDE via an integer value between 0 and 21.

Every pin can be used as a digital input or output, for blinking LEDs or reading button presses. The Pro Micro's I/O pins - 18 in all - are multi-talented. GND, of course, is the common, ground voltage (0V reference) for the system.The Pro Micro will remain 'off' until the reset line is pulled back to high. This pin is pulled high by a 10k&Ohm resistor on the board, and is active-low, so it must be connected to ground to initiate a reset. RST can be used to restart the Pro Micro.If the board is powered through the 'RAW' pin (or USB), this pin can be used as an output to supply other devices. This voltage is regulated by the voltage applied to the RAW pin. This voltage will depend on whether you're using a 3.3V/8MHz Pro Micro or a 5V/16MHz version, it'll be either 3.3V or 5V respectively. VCC is the voltage supplied to the on-board ATmega32U4.On the other hand, if the board is powered externally, through this pin, the applied voltage can be up to 12V. If the board is powered via USB, the voltage at this pin will be about 4.8V (USB's 5V minus a schottkey diode drop). RAW is the unregulated voltage input for the Pro Micro.There are a variety of power and power-related nets broken out: Delving a little further into which pins do what.

Arduino micro wire library pins