In order to add this feature to your cards, you need to manually edit the card type. There is an official Anki video here that will guide you through the process.
This is not enabled by default because it dramatically slows down your studying process and is an inefficient (and oftentimes unnecessary) way to learn spelling. Many of us find that spelling is acquired just fine without having to manually type in the words. If you find that you are having a difficult time picking up spelling, enabling this feature can help. You may find that after a period of time you can disable the spelling tests when you gain confidence in your knowledge of spelling in your target language.