Help…Can someone (PLEASE!) tell me how I reinstall the OS from DMG file

I have a Powerbook G4 Laptop and had to replace the HDD …and of course can’t find a disk to reinstall with so a friend gave me the OS on a flash drive which I can convert to an ISO or whatever I need too in order to get it to boot when I insert whatever I burn into my laptop …the question is PLEEEZE can some one walk me thru what I need to do real quickly (or slowly) THANK YOU!