Interestingly, the manual that I found online (which appears to be identical to mine) says that the normal stitch plate should be taken off and replaced with the darning one, but my manual says to put it on top, matching the pins into the holes, and clearly it wouldn't be possible to fix the darning plate in on mine as it doesn't have screw holes, and isn't the same shape as the normal one.
I did find a mention in the manual of the lights - 'When the needle is down the red indicator above the button will light up. When the needle is up the green indicator will light up.' The two lights are alternating very quickly on mine.
However, I didn't set the stitch length to zero (the manual doesn't tell me to, but I should have known anyway). I will try that shortly.