This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of dark? It's dark.
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're thrown into something dark and small. A lid is closed on top of you, and you are confused. What have you been thrown in? You find out you've been thrown in a cooler (くら). Feel afraid like you would be if you were thrown in such a dark cooler like this. Is it cold?
Can you make your iPhone screen a bit darker, please?
I heard that Mr. Tanaka has nyctophobia, so he can't sleep in a dark room.
Everything in the news has been depressing lately, but there is a great big silver lining to this dark cloud, you know. And... well... I kind of lost my train of thought, but, anyway, will you marry me?