Write your post in the textbox. You have numerous possibilites in order to edit your post:

• copy-paste the URL of a video,  a webpage, or other content types in the textbox and it will be automatically embedded and can be viewed within CooSpace
• attach file(s): you can find the 'Attach files' on the lower right section of the comment box. You can use two types of attachments - new files can be uploaded, and also files which are already uploaded into CooSpace (so they can be found in your personal documents or scene documents). By default, users can attach a maximum of 3 files (or 10 MBs) to one comment. If your attachment exceeds these limits, CooSpace will alert you and you may not be able to upload you files.
• edit the appearance of the text (make certain sections bold or italic, or set different styles).