My chickens had no trouble learning the nipple system. For the first few weeks, they drank from a small conventional waterer (Mason jar style.) Then, at about four or five weeks, I simply substituted a nipple drinker and showed them by holding them in my hand, and gently pushing their beak into the nipple until they got some water in their mouth and swallowed.
The two latest chicks didn't learn at the same pace, however. The little pullet "got it" right away and immediately understood that she had to peck at the metal valve release, but the cockerel seemed to think that pecking anywhere on the red plastic would release water. For the first couple of hours, he would wait for her to peck and release water, and then he would drink, but now he hits the "sweet spot" with no trouble.
I have been keeping my own chickens for only a year, and am still learning. Just last month, I started letting my year old flock out to free range more. In the past, they had to go back inside the coop to have access to the nipple drinkers, but this year, as an afterthought, I filled a two gallon bucket brimming full, and put it in the shade outside. They love it so much that I feel like I should have done it long ago. They gather around the bucket and drink like it's the best thing ever. I still prefer the nipple drinkers inside the coop, but plan to find a way to allow them freer access to water outdoors.