In addition to viewing presentations, as an attendee you are able to post comments on the presentation. 

Comments are recorded and listed as part of the presentations history. 

1. Click on the poster you would like to comment on.                                                     
2. At the top of the poster screen you will see the comment button  click on it and the Comments window will open.
3. Type your name in the name field.
4. Type your comment in the comment field.  
5. Click on Post to send the comment.
6. Your comment will now be visible to the presenter.