How to install Mac OS Snow Leopard in my Mac that doesn't boot up?

Hello Everyone,

Please help me. It has been a few months since my Macbook White (Late 2009) crashed and when I boot up, a blinking folder with question mark appears all the time. Now, I have accepted the fact that I will lose all my documents so I decided to make a bootable USB to clean install Snow Leopard. When I press "Alt" the laptop prompts me with a password which I do not know. Please help me how can I install the Snow Leopard using a falsh drive. Please I need a laptop to use 😟

Thank you.