Macbook a1181

Hi, i just recently bought a used white apple macbook a1181 from ebay. The macbook came without an operating system in it so now that i got it when i turn it on it just shows a blinking question mark in the middle. Can anyone tell me what operating system i need to buy for my macbook? I bought mac os x snow leopard 10.6.3 but i dont think that is the right one because when i put it in it does not do anything it still shows the blinking question mark.