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 put between, so the verb version is to put between or to sandwich.

挟む means to put something between two things, like putting ham between bread or catching your finger in a door (ouch). You'll also see it in phrases like 口を挟む (to butt in with your opinion) or 耳に挟む (to catch a rumor that "slips between" your ears).

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 so you should be able to read it!