At the bottom of your contest page sits a Comment area that can be seen by everyone who visits your contest.
This Comment area should be used for general comments about the contest — anything you want to say to everyone participating in and watching your contest.
You can leave private comments and feedback for individual designers in two ways:
Click the chat bubble icon beneath an entry on the contest. A comment box will appear where you can leave a comment that only that designer will be able to see.
On the fullscreen view of each entry, you’ll see a comment box. Again, you can use this to communicate with the designer directly, and see any replies they send you.