How do I know if 10.6 is right for my MAC? Where do I download it? Is it for free?
It costs 29 USD/GBP/EUR as "Update Version", which is actually a full version with update pricing. It's only sold on a DVD which you need to order from Apple or get from a retail store.
The system requirements are here. If you have a model produced since mid 2006, or a Macbook/Macbook Pro, you're good.