InHisLove -
Down below the reply that you would be typing, you will find a block called:
'Manage Attachments'
Click on that button and your CFS stored attachments will be on the list.
Click to open your attachment and hover over the one that you wish to include in your reply and 'copy' it.
Then paste that attachment into your reply. As long as the attachment is already IN the CFS server, it will be present in your reply.
I took the liberty of doing that in your reply just above this one to show you how it would end up.