I don't understand the instructions.
我不懂这些指令的意思。
I don't understand what you are talking about
我不明白你在说什么。
'I don't understand,' the Inspector mumbled, passing a hand through his hair
“我不明白，”巡官一边嘟囔道，一边用手捋了一下头发。
I don't understand how the two facts relate.
我不明白这两个事实有什么联系。
I don't understand what you're talking about.
我不懂你在说什么。