How do I turn on captions or change their size?

Press CC in the player, or set your language and size on the Devices tab.

In the player, press CC to show captions. To set them for every episode, go to Account Dashboard → Devices → Language & Accessibility and pick Subtitles (or Off) and Subtitle size (Small, Medium, or Large). If an episode has no captions, the player says so. Audio description is in the same place and plays where an episode has it.