When a vocab is a single kanji plus some okurigana (hiragana stuck on the end of kanji) it's almost always going to be the kun'yomi reading. This is one of two kun'yomi readings you'll be learning for the kanji 入. As long as you know that this vocab means to insert, you can use that to remember the reading as well.
Imagine inserting your hand into a hole and an eagle (い) flies out, screaming: "い!" This is something that happens every time you insert your hand into something: an eagle comes out. You don't know why.
What will you put in the square?
Please insert twelve pieces of origami paper here.
I put a hamburger into the coffin.