system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is fire made actually of? Is it even matter?
gpt
So there are some very different sources of light from a standard fire.

The first is from the chemical reaction itself.  Combustion is an oxidation reaction, where some element (usually carbon, in the fires that we're used to) combines with oxygen.  In a candle, this results in a pale blue flame close to the wick caused by "molecular radicals" that are excited, and emit light as their electrons fall back down to more stable orbitals.

The orange/yellow part of the flame is from an entirely different process.  If the fuel is incompletely burned, it will release some soot particles, which are mostly pure carbon (in the case of burning carbon, of course).  These will glow because of blackbody radiation (the same reason heated metal glows).

In more powerful flames, such as a Bunsen burner with an increased oxygen supply, the flame will be hotter than normal (as it is able to burn the fuel more completely), and this will result in a blue color as it ionizes the gasses around it.

So to summarize, fire is a chemical reaction that releases heat and light.  The light is what you perceive as "the fire", and it comes from several different origins depending on the type of flame.