There text areas in themes that are edited through the theme editor (e.g. section headings). To modify words and phrases without these theme editor controls, head over to the Edit languages settings.
The Edit languages settings allow merchants to directly change the labels, notes, or other text areas found throughout the theme.
For example, say a Startup merchant wanted to change the note on the cart page that says, 'Excluding tax and shipping'. They could go to Actions > Edit languages, open the Cart tab, then locate the Tax and shipping portion to modify the text included in this field.
More articles on the language editor
Using the theme language editor