Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
You go to open the door. When you do, a huge scream comes out: "AAAHHH!" (あ). Imagine giant あ characters flying out of the door you opened as well.
Please open your Japanese dictionary.
My boyfriend always opens the car door for me when I get in.
"Can you open this bottle of wine for me?" "Of course. Piece of cake."