I don't understand the instructions.

　　我不懂這些指令的意思。

　　I don't understand what you are talking about

　　我不明白你在說什么。

　　'I don't understand,' the Inspector mumbled, passing a hand through his hair

　　“我不明白，”巡官一邊嘟囔道，一邊用手捋了一下頭發。

　　I don't understand how the two facts relate.

　　我不明白這兩個事實有什么聯系。

　　I don't understand what you're talking about.

　　我不懂你在說什么。