I don't know how to interpret his words.
I couldn't figure out what he meant.
I don't understand the meaning of what he is saying.
I can't figure out what he is saying.
I cannot understand anything he said.
I can't understand anything he said.
I could not understand anything he said.
I can't think what he might say.
I didn't understand in the least what he said.
I can hardly understand what he says.
I can barely understand what he's saying.
I don't understand at all what he is saying.
I don't know understand why he said that.
I tried to understand what he was saying but I couldn't.
I don't quite understand what he says.
I cannot understand what he is driving at.
I couldn't seize the meaning of his remarks.
He cannot understand the report that I wrote.
His excuses represented nothing to me.
I could not understand anything he said.