You can turn closed captions on or off by clicking on the caption settings icon in the bottom right corner of the screen.
On some devices, this will simply toggle captions on or off. On other devices, you will an overlay menu with options.
In a web browser, you will will see a small pop-up menu where you can change your selection.
You can also change the appearance of your closed captions on web by clicking Subtitles Settings. That will bring up a settings menu like this: