Hexawise "Notes" allow you to add comments and/or questions to models
Notes are specific to individual models. They are located under Review in the left navigation pane.
Fill in the details of your note and click the "Create" button.
Keep in mind that anyone with access the model (including reviewers, etc.) can use this feature. This is usually a good thing.
How many notes have been created for a model? That information is shown in the red circle:
Click on the trashcan icon (appears on hover in the far right) to delete an existing note or on the pencil icon to edit it
Click "Yes" in the confirmation dialog to confirm the deletion.
Make sure to take good notes when designing your test models! You'd be surprised how much you forget by the time the next release comes around.