The chemical description of fire is a combustion reaction. It involves the reaction of oxygen with molecules in some combustible material. The fire itself is caused by energy released by this reaction in the form of heat and light. The fire you see is not only the light that’s being released, but also glowing hot gases.
Before matches and butane lighters were invented, people could use flint to start fires for heat and cooking. Striking a hard piece of metal against flint causes a spark, which can in turn catch tinder on fire.