Send A Note/Message With The Order
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.

When customers odder, they can now send a message or note.

Change short message pleaceholder text
To change the short message placeholder text, navigate to Ptoduct Table -> Configure page. Scroll down and you will see the "[Type your Message.] Message" input box. From there, you can change the placeholder text.

Chnage "Message" Text
First, take a look at the below image.

You can change the text "Message" also. You need to use a filter hook for that.