The phrase "sets fire to" typically refers to the act of deliberately starting a fire. There are several different synonyms that can be used to describe this action, including ignites, kindles, sparks, lights, and torches. Each of these words conveys the idea of starting a fire intentionally, whether through the use of a match, lighter, or some other means. Other words that can be used as synonyms for "sets fire to" include incinerates, burns, and scorches, which suggest a more destructive or intense level of flames. Whether you're describing a controlled burn or an act of arson, there are plenty of ways to talk about starting a fire in English.