According to EA, "The Sims 3" expansion packs cannot be played by themselves. Players must have the base game before installing an expansion packs.
Expansion packs do exactly what they say; they expand on top of an existing game. The expansion packs add new gameplay features and unique items to an existing installation of "Sims 3." Any combination of expansion packs and item packs can be used, but they all require a preexisting installation of "The Sims 3" to function. Copies of the base game can be purchased from retailers as physical discs or purchased on EA's Origin client as a digital download.