Well I was about to come and correct you as well.
But I shall not.
I will however teach you the ways of replying! You see, you sort of posted on your own wall. You have two options. Click on the users name or avatar and write on their wall. Or, you can click "View conversation" which is located at the bottom right, right next to the report button. There you can view your whole conversation with that person and reply as well.
Hope that helps.