Once you enable multiple languages on your StoreFront, a small globe will appear on any text input that supports translation.
When you click on the globe, an editor will come up showing you all of the translations for the given piece of text.
You can edit the English text or any of the translations. By default all of the translations will be auto translated on demand. If you want to immediately update the translations click the orange "auto translate" button. The text will translate on the fly and then the screen will update.