How do I add or edit text on a plot?

Use the Text tool which allows you to change the format, style, etc. of individual axis labels, in addition to the plot title and legend items. It can also be used to create new text labels anywhere on the plot or layout window.

Note: Due to adding support for Unicode, typing a Latin character in the Edit String dialog on the Mac and converting it to the Symbol font will not immediately display the Greek character. It will be displayed when you exit the dialog. It is possible to see the character immediately if you copy it from the Font Book application and paste it into the Edit String dialog.