How to create bootable installer USB for macOS in Windows?
I doubt you'll be able to do this. Even if you could find a URL to the OS installer app outside of the App Store, you can't run the installer in a Windows environment. 

2008 Macs didn't have Internet Recovery. However, it's usualy for them to have a  Recovery Partition on the internal drive, which you can access by restarting while holding Command and R. 

Did your friend sell you the Mac without an OS on the drive? I'd go back to him, if he has another Mac, and see if he can help. 

You can still buy OS X Snow Leopard (10.6) from Apple on a DVD. It's about US$20.