Detailed
Expert
い adjective
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 detailed? It's also detailed.
When something is detailed it is made up of a huge quantity (くわ) of little things. And if you're an expert on something, you'll have a huge quantity of knowledge, too.
ずい分シメサバについて詳しいんですね。
You are quite the expert on mackerel sushi.
すみませんが、私はじゅうについて詳しくないので下手に触らない方がいいと思います。
I'm sorry, but I'm not an expert when it comes to guns, so it would be better if I didn't touch them.
「おお、そういえば、あいつら結婚するって聞いた？」「おお、マジかよ？ 詳しく教えてくれよ。」
"Oh, by the way, did you hear they’re getting married?" "Wow! Really? Tell me everything."