The pins are ultimately the screw terminals on your breakout board. For example in the photo you can see estop and home. It would help if you could upload a photo of the whole board.
You are looking for a screw terminal with the label step and the label direction. These send signals out to the drivers to turn the motors.
So to follow Doddys help touch one probe of the multimeter onto the screw terminal marked direction for the axis that should be moving and the other onto something marked ground. When you use the keys to go left and right that terminal should switch between 0V and 5V.