There are 2 types of soda, the green soda and the purple soda.
You usually see the purple soda when you need to move the bear to the top of the board past the candy string. The top of the purple soda is the highest point the bear can travel. You need to pop soda bottles to make the soda level rise.
The green soda is similar to the purple soda. The difference is that when you swap candies inside the green soda, any space affected will release one fish.