* "Épeler" is the most common and general way to say "to spell". For example: "Peux-tu épeler ton nom ?" (Can you spell your name?)
* "Orthographier" is more formal and means "to spell" in the sense of writing correctly. For example: "Il faut orthographier correctement les mots." (You have to spell words correctly.)
* "Dictée" can be used to describe the act of spelling words dictated to you. For example: "Nous avons eu une dictée aujourd'hui." (We had a dictation today.)
The best way to choose the right translation depends on the specific context.