When making a fire, without gas, matches, or a lighter, what are two important things about the wood?

The reason wood burns more easily than most metals is because it doesn't actually burn, it vaporizes instead. When wood is heated, the molecules in the wood break down to form flammable gasses, which mix with the air and then burn. Then it takes more heat energy to trigger the reaction with oxygen. The amount of heat produced depends on the molecules that make up the fuel ... For example, large pieces of wood take a lot longer to absorb heat energy to ignition temperature. A twig catches fire easily because it heats up easily

that is a solid and that there are other ways to make a fire?