what's what

基本解释

He will tell you what's what .
他会把事情的底细告诉你的。
With so many things mixed up, it's hard to make out what's what.
许多问题绞在一起，闹不清楚。
《新英汉大辞典》
Language English, so you have to translate in order to understand fully what's what, I just described what I understood from the description of the file.
语言英语，所以你必须翻译，以便充分理解什么是什么，我只是描述了我从该文件的描述理解。

"We looked at a very high resolution picture of the brain, where we can actually measure what's called cortical thickness.
People who came by land you would be hearing rumblings about down the road from villages that were spread out, but if somebody comes in from the sea on a ship, you may find them there in the morning and you don't know what's what.
陆上来客总伴随着车马隆隆声,沿着途经的村庄一路传来,但是如果有人乘船从海上到来,当他早上来到时你会发现,你对他一无所知
耶鲁公开课 - 古希腊历史简介课程节选
most of it is really a kind of high-end stuff. You can see, you know, what's trendy, what's new there,
其中很多商品真是高品质的。你可以看得到，流行的、新潮的东西，
小心超额消费 - SpeakingMax英语口语达人

That's where the guys talk about what's in the news, what's on their minds.
NPR: Could The President's Week Get Any Worse?