I had never went either, and well, I'm a water chicken

(I can swim but not crazy about water over my head.!)
My DH had gone before, and really, its pretty easy, you sort of float on the top of the water, or you can kick down to to floor of the water area (thats a little tricky)
the depth does get deeper, especially in the coral reef (It was over my head), but really the vest keeps you afloat well. (you wont sink or anything)
It really was pretty simple, put face in, and breath with the mouth piece.
Its so pretty, and relaxing, and really really gorgeous, you kind of forget about the depth/tempature of the water.