Hi Elena!
You can turn on subtitles by clicking the small box with "CC" in it, usually found on the bottom right of the film. If that button is not there, then the title does not have any subtitles available at that time. If the button is there and you click that box to turn on the subtitles, it will tell you what languages are available. If there is more than one language available for the subtitles, then it will list all the options and you can choose which one you want. A good example is The Torchlighters. There are multiple different subtitle language options for that series!