Members of the public community cannot add attachments. Members of the MOSC community can. It's usually best to post all relevant information in the body of the message. Not everyone's fancy to download people's attachments.
The attach link in my replies is not present? Is there something to set in my profile or similar to enable attachments? Id post a screen shot but sadly, I cant post attachments :0)
You can post screenshots by clicking on the "Insert Image" icon in the editor and selecting the image you want from your computer, which will then be uploaded directly in to the post.