The 4 day course is to become a certified diver, you also have the option of a resort course. A resort course will allow you to dive with an instructor to around 35'. You start with an instructional video, learn some basic skills, then you're off!
I'm a newly certified diver and the friend I went with did the resort course at Amigos del Mar. I tagged along for the instruction and we did our diving together. We were both thrilled with the experience.
The price was VERY reasonable.