"The butterfly enters through the open window."
Translation:La farfalla entra per la finestra aperta.
I made that mistake too. I did because it was the translation for "the water is coming through the roof". Probably "da" means "from above" and "per" means "through".
tomerjar: I believe that "nella", or any contraction meaning the english "in the", actually refers to a noun being physically inside another noun. The butterfly in this case is not physically inside the window itself as an object, but merely passing through it. I may be wrong about this, however, I feel very positive that this is the italian meaning.
OUMEN: The preposition "verso" means "to" or "toward". In this sentence the butterfly would not enter toward the window, but enter through the window. At least this is my understanding.