You can send Orders Notes directly to your customers if they have provided an email address during the order process.
First, go into the Orders table and click on the order you want to manage (I have chosen order #9000005 the latest one for this example).
Once inside the Order, look to the bottom of the center column.
Here you will find the Order Notes field.
Simply type in your desired note and click Add A Note. This can be a note you want to just leave on the order or a note you would like to send to your customer later.
Your note is now on the order. To send this order note to your customer, simply press the green envelope icon. To Show this order note on the invoice, press the grey eye icon, to delete it, press the red bin icon.
Before your message is sent, a final confirmation pop-up will appear. If you want to continue, just press OK and your message will go out to your customer.