Comments can be left on orders for you, your team, and even for your customers. To do that, look for the Show Comments button at the bottom of an order page.
Clicking on that will then open up a comments box where you can type your comment in. You'll see options for making a comment internal, public, or private.
Internal - Your team members will be able to see the comment.
Public - Everyone who has access to the order can see the comment, including your team members and customers.
Private - Only you can see the comment. Perfect for leaving yourself notes regarding an order.