The difference between snorkeling and scuba diving is the level of equipment-assistance. Sometimes, snorkeling is also call skin diving; basically, the diver will use very limited equipment such as a snorkel, mask and fins. They normally dive in shallow water near the shore; the time they dive is the time they could hold their breath. They don't really need to learn and they don't need a license to do so. Scuba means Self Contained Underwater Breathing Apparatuses. The most obvious difference is the air-tank at the back of those divers. They dive into the water by breathing from an air-tank contains compressed air which pressure could be as high as 3000 p.s.i.. They could dive up to 130 ft in terms of safe range for non-mixed gas. Scuba diving need training and almost all dive shops would not rent gear or allowing non-trained person to be engaged in such activity because a license to do so.
I am a diving instructor