The e-mail above is information on how to get from the International Airport (mainland, where you arrive in country) to the water-taxi area in Belize City, and thence by water taxi to either CC or AC. To catch the water taxi to CC from San Pedro, go to the pier by the Tackle Box in the heart of San Pedro.
Check the CC schedule and then go when you like.
The tour with three snorkel stops and a lunch stop at CC is a pretty good deal - you'll probably be doing snorkeling during your visit anyway, so this is a way to combine adventures. If you are concerned enough about water-safety to wear a life-vest when swimming, it might be best for your to do most of your water activities in the company of a good guide - they are trained to take care of you and show you things you would not see on your own. The local tour guides are great company - you get a chance to learn about local things and make a new friend. I also recommend the Rainbow on CC for lunch .......... love that place!