Never buy a computer without the discs it shipped with from the factory, and if the system has been upgraded since, without the install discs for system it has now.
If you can't find system preferences on the hard drive (try with Spotlight), get Snow Leopard. MacBook will run it fine, and you'll have not only the discs but a newer system (for much cheaper than getting the replacement discs, and it will be good to have those discs anyway for any possible disaster or recovery need in future).