There is a pretty good demo at the following URL:
The demo shows how to display the fileUpload component, as well as a preview for what is uploaded. What it doesn't cover is turning the uploaded files into attachments. When you click submit the action should grab the list of Files that exists in the backing bean and add them to your emails attachments. I don't have the javamail API in front of me so I'm unsure what format attachments need to be in, but you should be able to just add the bytes to the email.