I like having funny sentences to translate. Somehow it's funnier when you don't know what it means right away and you have to piece together what it means.
Nauraa can be translated as 'laughs/is laughing' and also as 'to laugh'. The former is used whenever the subject is singular and neither 'I' nor 'you'.
So "He laughs": Hän nauraa. "The woman laughs": Nainen nauraa. "A baby is laughing": Vauva nauraa". But "I laugh": (Minä) nauran. "You laugh": (Sinä) naurat.
This is taught in the tips: https://www.duolingo.com/skill/fi/family/tips-and-notes.