To Stop
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 means stop, so the verb 止まる means to stop.
But this is the intransitive version, so it doesn't take a direct object. A train stops, or you stop at a red light. See? No direct object. You can remember this because you often have to stop when you see a 丸 (まる), a.k.a. a circle. Think about it — red lights, the cancel symbol, and no trespassing signs are all 丸. Even stop signs are… sort of 丸?
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You learned this reading when you learned the 止める, so you should be able to read it already!
この白いラインで車が止まる。
Cars stop at this white line.
スケートリンクの上で、止まることができなかった。
I couldn't stop on the skating rink.
バスは、もう少しで止まりそうでした。
The bus almost stopped.