I just want to say if you are very unfit you need to take things SLOWLY at first until you feel more comfortable doing more. Now the first way to use zumba for fitness and this is especially if you are very unfit is to practice at home, spend ten to fifteen minutes say three times a day practicing the moves. You are not going to be use to it and they are going to be going faster but do not worry just get a feel for it and do it to your own time. Over time you will get faster and better, just have fun. Feel the beat and move those feet, you will feel energized from shakin that body.
Secondly you could join a zumba group, their are plenty around and you can check in your local paper or gym. I would only move on to this next stage once I felt comfortable knowing the basic moves. Many people take these classes at all fitness levels so you have no need to worry about what stage you are at. It's just about having fun and meeting new people and that's all good. Also remember everyone is their to have fun and get fit, so enjoy.
My last way of using zumba for fitness is to get together with your friends and have a zumba party. How much fun would that be? Send out invitations to a zumba party, come in loose clothing, bringing some healthy nibbles and zumba. When you have had enough of zumba just enjoy the rest of the day with your friends. It's a day to have fun and all that wonderful music will create a wonderful atmosphere. Using zumba for fitness is a great way to get active and have some fun.