How do you stay underwater while snorkeling?
Lift your feet above your head and straighten your legs so that you descend vertically head first. Do not kick your fins until they are under the water. You can use a breast stroke with your arms to aid propulsion. Keep your snorkel in your mouth.
Is it possible to breathe underwater?
Humans cannot breathe underwater because our lungs do not have enough surface area to absorb enough oxygen from water, and the lining in our lungs is adapted to handle air rather than water. However, there have been experiments with humans breathing other liquids, like fluorocarbons.