Try this for a quick and simple batch of soda. This was the first batch I ever made, and boy was it good. Drinkable in about 20 hours too!
Clean and sanitize everything as usual. Warm 2 Liters(or however big of a batch you want to make) of water in a pot, or microwave, or over a fire, or with your mind. Mix in sugar until it tastes yummy. You're basically making simple syrup here, which is a mixture of 2 parts sugar to 1 part water. This will make it very sweet(too sweet), so you don't need to make 2:1 you should make 1:1 or even less, just add sugar until it's to your liking. Add a few splashes of vanilla extract, again to your liking. Once sugar is completely dissolved in water, remove from heat and let cool to a little warmer than room temperature. Drop in 1/4tsp of yeast for every 2 liters, or every 8 cups, of water. You can also drop in some acid blend or a little lemon juice if you have any on hand, I used about 2 Tbsp acid blend. Once this is all mixed in there, pour into your plastic soda bottles until you have an inch of headspace, then squeeze the bottle so the liquid comes all the way to the top and put a cap on it. You do this to get out the extra oxygen and give room for the co2 to expand. Next, put the bottles someplace where they will be okay if they explode. After about 12 hours, the bottles should feel very firm from the expanding co2. Once they are firm put them all into a fridge to stop the yeasties. After a few hours, or whenever they are cold enough, they are drinkable.
The first time I made this it came out very sweet. I used 34 cups of water(roughly 8 liters), and 2 lbs of sugar(about 8 cups). I probably used about 1/4 cup of vanilla, as I just kept adding it until it was the color I wanted. I probably could've used 1 part sugar to 4 parts water, which for a 2 liter batch would be 8 cups of water and 2 cups of sugar. Now I'm experimenting with carbonating crystal light drinks, as they are cheap, pre-sweetened, and have many different flavors which would lend well to carbonation.