It's fairly simple to begin carbonating things; here's a list of the things you'll need to follow this instructable step by step:
-CO2 supply: This can vary greatly between setups. I use a 20# tank, but you can use nearly any size CO2 tank with a regulator. Heck, I've even used 9-20oz paintball tanks to carbonate things! You can find good used 20# tanks on eBay (I got mine for around $40)
-A Regulator -this is a good one.
-To carbonate liquids, you'll need an empty 3L soda bottle.
-A clamp-in schrader valve for the 3L soda bottle - you can find these at nearly any auto parts store. Here's one that will work. Here's another.
-To carbonate fruits and other objects that you can't pour, you'll need to build a pressure vessel out of PVC pipe and other standard fittings that can be found any hardware store. This will be discussed in detail later in the instructable.