In ancient times,people used to start a fire by friction.For this purpose,they would continously rub two sticks together.
Ideally, you’d keep a fire going rather than lighting a new one. Even if you just had a few embers, it wasn’t difficult to throw some kindling on that and build a fire up again. However, if you had to start a fresh fire, there were a few techniques:
Friction. The “rub two sticks together” approach is probably most common through history, though it could be vastly more sophisticated than that. Ideally, you’d have a hardwood stick and rub or spin the point on a softwood block. This might mean rubbing it up and down a groove in a block of wood or spinning it by hand or with a bow drill in a hole in a prepared block. This both generated heat by friction and produced a quantity of easily kindled fine sawdust.
Sparks: Striking iron or iron pyrites against flint or similar stones creates short-lived but high-temperature sparks, which can be directed against kindling.
Pressure: This wasn’t widely used, but some societies in Medieval southeast Asia took advantage of ideal gas laws before they knew what those were. They used a device consisting of a small cylinder closed at one end and a tightly fitting piston. You’d put a scrap of kindling in the bottom of the cylinder, then slap the piston in. Ideally, pressure increases sharply in the airtight cylinder, which naturally increases temperature enough to set the kindling alight.
Once you’ve got a tiny, glowing ember, all methods start to look pretty much alike. The ember is applied to something very dry and very finely divided (sawdust, wood shavings, willow fluff, etc.; kindling might be treated with sulfur, nitrates, waxes, and other flammable substances to help it catch fire better), which is easy to set alight. One you’ve got that going, you can light something more substantial (a splinter or twig), and then on to light a useful fire.