I don't understand what you said
看不懂───I don't understand;说───say
I don't understand what he's saying.───我不明白他在说些什么。
I don't understand the instructions.───我不懂这些指令的意思。
I don't understand what I have to do.───我的确不明白我该做什么。
Anything that I don't understand, where I have to make the leap myself in my own head, is going to stop the flow of the presentation.───任何让我不理解。任何让我需要我自己去猜测的，都会让这个演讲不流畅。
I don't understand exactly what you are trying to say.───我不很了解你想说什么。
The man shook his head. "I don't understand the question, " he said.───男人摇了摇头，“我不明白你的意思，”他说。
I don't understand what you're trying to say.
I don't understand very well.
I don't understand. You'll have to elucidate.
I don't understand how the two ideas relate.
I don't understand this book--I can see no sense in it.