Once you have original language captions for a project, you'll be able to create new versions for translation.
To do that, click on the Translations tab, and click on the Add button. This will pull up a list of the languages available for your team.
You'll be able to select which languages you wish to create a translated caption set for. You can use the "Select All" or "Select None" shortcuts to make it easier to choose languages.
You also have the option here to automatically translate your captions. This will send translations to the default translation provider (currently Google Translate), and return translated captions. You can then assign linguists to review and improve these translations.