Put your nose to the cut out in the jig and your eyes will be aligned with a series of lights on either side, which will illuminate randomly in either red, green or yellow hues. Just call out the colour you see without moving your head or eyes (the lady sits opposite you to check for movement and will knack you if you do) and as soon as you reel off a few correct answers, you're done.
Except wifey who struggled and we couldn't work out why, until later, when she realised she had on her best glasses. These have quite thick arms which were directly in her eye line and were blocking her sight. She managed it fine in the end but bear this in mind when/if you wear glasses, take them off or wear thin frames.