"no" or "na" is the contraction of "em + o" and "em + a".. it's the same that "in + the" or "at".. but in portuguese, "na" and "no" will depend of the gender of your speech.. "na" for female words, "no" for male words.. eu deixei meu celular no quarto/I left my cellphone in the room.. "quarto" is male word.. minha mãe está na cozinha/ my mom is in the kitchen.. "cozinha" is a female word..