That we extract the liquefied remains of ancient forests, animals and sea creatures out of the earth, refine them so they are hugely flammable and explosive, pour it into canisters and then ride around on top of them igniting the liquefied remains of said ancient animals thus making the car wheels go round. Or pour them into power plants and burn them.
Whenever people complain about net zero and green energy, that means - back to the liquefied ancient animals.