The Holiday is an older ship, probably the oldest one Carnival currently has. I take it you chose Mobile because it's nearby? You might have a better choice of some nicer ships if you are willing to cruise from New Orleans (assuming you are driving distance from Mobile), or from Florida ports. I've seen Holiday - she's ok, but there are much better available!
I agree with "luxury lady" that you should start by visiting a good local travel agent. If you don't have one you like working with, ask your friends & neighbors, folks at work, etc. for recommendations. Booking online is a possibility, but for a first cruise, it's much better to work with a professional who knows cruises and can help you find one that you will enjoy!