请问I don't understand you said.和I don't understand what you said.两句有哪些区别?或者有什么错...

请问I don't understand you said.和I don't understand what you said.两句有哪些区别?或者有什么错...
请问I don't understand you said.和I don't understand what you said.两句有哪些区别?或者有什么错误请帮忙改正,改正后顺便解释下语法,