There are multiple grocers that sell soda that you could go to. They will depend on your location. Some of them include Kroger, Giant, Martin's etc. (Just google grocery stores near "your location" and results with directions will come up) ;)
Walmart, Target or any large retail store as well as your local grocery. All these should have both 2 litre as well as 12 oz bottles and cans in 12, 24 and 32 oz packs. Places like Sams or Costco usually have a more limited selection but offer large quantities of cans for a good price.
if you are asking about an actual soda fountain thatll be more expensive. Youll either have to buy one or rent one from a cateret or party supply place and that will include syrup and carbinated water plus the cost of cups and ice.
Close your eyes and ask the soda fairy to bring you some! Just ask your parents.... As far as anything else you should know but clearly don't, again, ask your parents. How old are you? How is it that you can obviously work a computer or phone, but you don't know where soda can be purchased? Geez, you must live a very sheltered life where you have maids to bring you everything and do everything for you!!!
What can i say 2 u that hasn't already been said here....,wow,really? @ least i can welcome u to our planet EARTH & when u find ur "soda", please try not to get overwhelmed by what may seem an unlimited amount of choices. Go for 2 or 3 different kinds to start you off on your first time. I would hate 2read that your brain short-circuited somewhere due 2 system overload!