You don't need a CO2 system, unless you have very bright lights. What kind of lighting do you have on the tank (watts)?
CO2 is usually the factor that limits plant growth in aquariums, though, so it's a great thing to add. There are many ways to add CO2, from so-called liquid carbon (such as Seachem Flourish Excel) to yeast-based DIY systems and pressurized CO2 supply. Liquid carbon would be a good way to start. Plants will also benefit from added macronutrients (nitrogen, potassium, phosphorus) and micronutrients (trace elements); you can find these from several manufacturers, and some products like Tropica's TPN+ contain everything you need.
With that out of the way, I'll point out that there are many plants that'll do just fine in a low-light community tank with a sand substrate, without adding any form of CO2 or ferts. They'll just grow more slowly. Depending on your tap water, some plants may experience micronutrient deficiencies though. One succesful way of low-tech planted tank keeping is to dose micronutrients only (Tropica's TPN without the plus sign, for example).