Well good for you! you are about to take your first steps into a larger world. I will not bore you with the cenote geography, you can lok that up on the Internet at any time. However you book the trip, cenote dives are worthwhile. This is how it went for me both times. After reporting to the dive op, did the usual don’t blame me if you croak paperwork (ha, ha, ha), paid the fee, and met the guide. The guide is a full cave certified diver, you won’t go w/ anybody less certified than that. Load up onto a vehicle, usually a p/up truck w/ the gear, and off you go. During the drive there will be the usual introductions, the guide give you his working background, history of the cenote and the surrounding area, signals to acknowledge and follow, emergency procedures, how the route is marked, what you expect to see, how to check buoyancy and other areas related to the day’s dive. When you get to the site there’s an entrance fee to be paid by the guide and off to the site you go w/in walking distance after parking.
Get your gear ready and any questions to the guide will be answered. At the cenote entrance final preps are made, jump in the water, buoyancy check, lights check, and go explore! Be prepared as I did to "WHOAAAA, how did these dang Mayans travel through this?" Hope this helps a bit.
Seawolf5