In Portuguese, they indicate that a syllable is stressed and alternate ways to say the vowels. e.g. "país" is stressed in "i" and means "country", while "pais" is stressed in "a" and means "parents". Tilde (~) indicates that the vowel is nasal, e.g. the "ã" in "São Paulo" means that it sounds like the "u" in "sun"; the default sound of "a" in Portuguese is the same as in "car".