You can leave public comments for everyone who visits your contests, as well as private comments that can only be seen by the designer who created the design you’re commenting on.
Simply click the Messages tab on your contest page and there is the option to Message all designers.
The Message all designers 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 a few different ways, which are listed below with supporting screenshots:
1. By clicking an entry which will show the design entry full screen.
2. Once the design is enlarged, a comment box will be on the right hand side of the page. (see below) Here you can leave a comment that only that designer will be able to see.
3. You can also leave a comment directly on a portion of the design that you want changed. Simply click on the design while in it's enlarged state as directed in #1 above.
Then a comment box will appear (see 2nd screenshot below) which allows you to leave feedback about that specific area.
Pro Tip: You can also view all of your private communication with a designer and continue to communicate with them by clicking the Messages tab on your contest page and then clicking each designers username.