Cancun

[DRE]

The difference between caves and caverns is that in a cavern you shuold be able to see daylight at all times, whereas with a cave that's not the case. This also implies that you should have direct access to the surface at all times in a cavern.
Cavern training consists of optimizing gear, learning how to run a guideline, the importance of redundant lighting, proper bouyancy skills and posture, the ecology of different types of caverns, and most importantly: to never, ever, ever go into a cave without further training (unless you have a desire to die, and then I'd recommend jumping in front of a train so that trained cavedivers won't have to pull your stupid *** out of a cave).
Cavern training is usually a 2-day 4-dives course involving some class room work and land drills, unless you decide to go for the PADI cavern cert, which you get for looking at a cavern in a magazine.