The Add Response button in a question determines, if you are unsure on the question being asked and you want to find out more details about the question.
You are able to ask questions and add attachments, this will not complete the action that has been created it will change the status of the action to Responded to Query , it will send an email out to the user that has asked the question explaining that there has been a response on the question they have asked.
If you are unable to follow these instructions, you may not have the required user permissions. Please contact your Site Administrator.