You understand the words, but you still don't know what the person means.
For example, you hear “Like my back is against the wall.”
You understand the words, but you don't understand the meaning. The speaker is sitting in a chair across the table from you, not standing against the wall.
You can explain, “I'm sorry, but I don't understand what that means”
Then you can ask, “Could you please use different words?" or
“Could you please explain what you mean?”
She then explains to you, "I don't have a choice any more. I have to deal with the situation."
You understand now!