On Dashboard, choose Make a To-do… in a note's More menu, or right-click a note (press and hold it on a phone or tablet). In Notes, it is in the open note's More menu and in the ⋯ menu on each note in the list.
The New To-do window opens with the note's title in the field and Today chosen. Change either if you need to, then press Enter. The To-do is added to the note's team and shows a link back to the note, such as "Note: Book the venue". The note is not changed.