How does one go about making a petrol bomb?
One doesn’t. A petrol bomb is an extremely crude bomb which has a disproportionately large chance of going wrong and setting fire to the thrower instead of the intended target. Those who are stupid enough to make them use a glass bottle half full of gasoline, with a rag soaked in gasoline pushed in as a wick. Light the wick, throw the bottle and the glass shatters on the target setting the gasoline alight.