As a kid, i was always fascinated with flames. I know that this is common among many children, but i was so fascinated, that i really wanted to learn what fire is in its core. The lack of internet and the difficulty to dig knowledge let me with the question for many years.
Nowadays, learning what fire really is is as simple as a search in youtube. The difficult part is to born the question rather than to answer it. Anyway, here is a short video that clearly explains what fire is.
Bonus video - How fire behaves in space. Not to mention that when i was a kid, it was impossible to find any video to explain this question...
NASA's Flame Extinguishment Experiment (FLEX) has been studying fire in microgravity aboard the ISS. Flame producing temperatures, flare-up oxygen levels as well as volatile liquid behavior all differ in space as compared to Earth: