We use the attached physical General Purpose Input/Output (GPIO) pin numbering system. Note that pin #1 is closest to the SD card slot. If you flipped this image 180 degrees, then it would directly map to how you view the pins with Piper (as seen further down):
And here it is from the Piper perspective ...
For example, the 5th and 6th pins from the left in the row closest to you (in the Piper orientation) are pins #32 and #30, respectively. These are the two pins that you wire up to move forward in the game!