Snuba is like a cross between snorkeling and scuba. You don’t have to do any training classes beforehand; you get about 10-15 minutes of training on the boat, which is sufficient. You wear a regulator that you breathe through, which has a tube connecting you to a floating raft above that holds your air. If you get tired, or otherwise want a break, you can always come up to the surface and hang onto the straps on the raft for a while.
I had trouble from the very beginning, hanging on the side of the boat, practicing putting my face in the water and breathing. The guide had told us over and over to ‘trust the regulator,’ and there was no reason I shouldn’t have been able to breathe normally, but I kept feeling like I wasn’t getting enough air. He noticed that I had my face out of the water at one point (while he was getting someone else settled), and asked if I was okay, and I told him that I knew I was getting enough air, but felt like I wasn’t.
He said to try focusing on the fish, the colors and movement, instead of thinking about my breathing. He was very calm and matter-of-fact about it, like it was no big deal that I couldn’t breathe right, and that helped with the anxiety. I put my face back in, focused on the fish, and after a bit, I got the hang of actually breathing through the regulator. Probably a little faster than would be ideal (it uses up more oxygen), but sufficient unto the day.
The trickiest thing is managing pressure — even though we weren’t going very deep at all, maybe 10-15 feet, descending you had to stop every few feet, pinch your nose, and blow air out of your ears, so they acclimated. The guide stays with you as you go through this process, checking to make sure you’re all right, but it does mean that if you go up or down much once you’re under the water, you need to manage that, which I found challenging. In the end, my right ear started to hurt, and I was very tired by then, so I gave up a little before the end of the dive and came out. I think I was under for about 45 minutes, though, which was most of the length.
It’s hard for me to judge the experience fairly, honestly, because as said before, I was cold and tired by then, and anxious about the new experience, worried that I wouldn’t be able to handle everything there was to learn (glad we did the snorkel first, that helped), and that I would be a nuisance to the guide, the others on the tour, etc. You don’t want to be the person who swallows a bunch of ocean and ruins the trip for everyone.
But I did it, and I would do it again, on a warmer day, when I was ideally in somewhat better shape and less tired to start out. It was a lot to think about, managing the depth changes and the water getting in the mask, and actually, the breathing I mostly forgot about once I got the hang of it, but still. I’m sure with practice, many of those things would become instinctive, and you could just relax and float and enjoy the experience. It’s a shame that for so many of life’s interesting experiences, the hardest part by far is at the beginning — it applies to learning to knit as much as snuba. 
Getting up close to a giant sea turtle was pretty damn amazing, though — being down at the bottom with him, and then swimming up to the surface. Worth the price of admission, in both effort and fear. Nemo and Dory would’ve been proud of me. Just keep swimming, just keep swimming…