Os x version 10.6

So I haven't used my old macbook in some time. However, I need to back up my iphone. In order to do that I needed to update itunes. In order to update itunes I needed to update my OS. Yet, I cannot update my laptop with 10.6.8 b/c a notification comes up that says my system requires 10.6. I cannot seem to find 10.6. Is this usual?

Sorry if this is a stupid question, but this macbook is old and I need to replace it. That's why I don't keep up with my mac updates.

Thanks