To Burn
To Be Lighted, To Be Lit, To Be Burning
intransitive verb, godan verb
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means lamp, so the verb version is to burn or to be lit. Just like what you'd do with a lamp.
ともる
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You haven't learned this reading yet, so here's a mnemonic to help you:
Who wanted the candle to be lit? Tom (とも) Cruise. He's afraid of the dark so he always wants all the lights and candles in the house to be burning at all times.
あの部屋に明かりが灯るのを見たんだ。
I can see light burning in that room.