the ins and outs
noun [ plural ] uk/ˌɪnz ənd ˈaʊts/ us/ˌɪnz ənd ˈaʊts/
C2 详情，细节
the detailed or complicated facts of something
I know how to use computers, but I don't really understand the ins and outs of how they work. 我会用电脑，但不太明白它的工作原理。