Hot
い adjective
あつい
おふろを四十一度まで熱くしてください。
Please heat the bath to forty-one degrees.
お茶をいれようかと思うんですけど、熱いのとつめたいの、どっちがいいですか。
I'm planning to brew some tea. Would you prefer hot or cold?
「どうぞ、お熱いうちにお召し上がりくださいね。」「有難うございます。でも、ええっと、ちょっと熱すぎるので、まだ食べられません。」
"Please eat it while it’s hot." "Thank you, but... well, it’s so hot that we can’t eat it yet."
This is for when a thing is hot, making this word hot thing. When the weather is hot that's 暑い. This is when you touch something and you burn yourself.
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: This has the same reading as 暑い, so if you've learned that you'll know how to read this word as well. If you haven't run into that word, you've probably run into the kanji 暑 at least. That uses the reading あつ. Two similar concepts, but there are two kanji to differentiate, which gets confusing.