Hola, yes, normally in Spanish the adjective goes after the noun, that's what you should learn at the beginning. Although is possible to use it before the noun, but yes, it matters. Sometimes the position of the adjective can change the meaning like "El libro grande" and "El gran libro". In your example "Ella es una buena cantante", you put the adjective first to emphasize it. "buena" is the important word in the sentence. Adiós

the right answer is Ella es una buena cantante Buena or buen (depending on th gender) is one of the few adjectives that are going to be placed before the noun. because usually in spanish the adjective goes after Exemple: buena cantante, buen cantante, buena apariencia, buena persona. I hope that helps you. saludos!