If breathing is suddenly difficult, the oxygen (O2) mask will descend from the overhead compartments downward towards your mouth. When reaching for the yellow cone, do not tug at it forcibly or you risk suture between the oxygen tube and the aircraft.

Take the oxygen mask and assemble it  by inserting the plastic strips in a row next to the cone, and tightening the straps from the front to the back of your head.  The arrows point to the right or left of your mouth depending on the direction you are facing. Your own experience of the cone may vary.

Put it on, and then assist your child. If the plastic tubing is tangled, your child will be deprived of the oxygen flow.  If the mask is adjusted too tightly around the nose and mouth, the oxygen will not flow.

If the oxygen is not flowing and your child is not breathing, release any kinks in the plastic tubing by smoothing it between your thumb and forefinger. Do not smoke while performing this procedure or you will be penalized to the fullest extent of the law. It is against the law to smoke in the lavatory.

Story of a Descent, part two