know what's what
US /noʊ wʌts wʌt/
UK /noʊ wʌts wʌt/

1.
知道是怎麼回事, 了解情況
to have a good understanding of a situation or of how things work
:
•
She's been in this business for years, so she really knows what's what.
她在這個行業多年,所以她真的知道是怎麼回事。
•
You need to spend some time learning the ropes if you want to know what's what around here.
如果你想在這裡知道是怎麼回事,你需要花一些時間學習竅門。