When a customer places an order, you can take a note or a short message from them. We have a column "Short Message (message)" for that. Enable that column.
Now when customers odder, they can send a message or note.
Change short message pleaceholder text
To change short message placeholder text, navigate to Ptoduct Table -> Configure page. Scroll down and you will see "[Type your Message.] Message" input box. Form there you can change placeholder text.
Chnage "Message" Text
First, take a look below image
You can change the text "Message" also. For that, you need to use a filter hook.