Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means abstain and the verb vocab version is to abstain as well!

控える is super versatile. It can mean to refrain from drinking, to hold back comments, or to stand by (abstaining from taking action). In some contexts, it can even mean "to take a memo" because memo-taking is like putting information on standby!

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 already, good for you!