A great place to start is reading all the stickies in the Weight Loss support forum, the Calorie Counting forum, and the Carb Counting forums. That will clear up a lot of your questions, and then I am sure people will be happy to help clarify some things.
You could also go to a calorie-counting website like
www.thedailyplate.com , enter your information and then play around with it. It will give you a calorie "limit" to lose weight assuming no exercise. You can then enter foods to see what you could eat in what quantities to stay in that limit.
The good news about just starting is that when you are very heavy, you can eat quite a bit and still lose weight. So in the beginning, it's quite possible you could still have a soda a day. When you've lost a good amount of weight, you may have to reassess, but by then you will have had success to motivate you.