I don't need to know the specifics of what happened, tell me why you made a mistake in one word.
I don't need the small details, tell me concisely why you made a mistake.
Don't give me the particulars. In short, why did you make a mistake?
"I don't need to know the specifics of what happened, tell me why you made a mistake in one word."=「何があったかの詳細は知る必要がないから、なぜミスをしたのか一言で教えて。」
specifics = 詳細、具体的な
in one word (sentence) = 一言で
"I don't need the small details, tell me concisely why you made a mistake."＝「細かい事はいいから、なぜミスをしたのか簡潔に教えて。」
（small） details = 細かい情報、詳細
concisely = 簡潔に、的確に
"Don't give me the particulars. In short, why did you make a mistake?"=「詳細はいいから、早い話なぜミスをしたの？」
particulars = 詳細、いきさつ
in short = 早い話、簡単に（手短に）言えば、つまり
"I don't need to know the specifics of what happened nor the reasons (excuses). First, tell me why you made a mistake in one sentence. I will ask you if I need to know more, so don't give me the detailed explanation."
日本 
