know what's what
US /noʊ wʌts wʌt/
UK /noʊ wʌts wʌt/
1.
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.
•
You need to spend some time learning the ropes if you want to know what's what around here.