Às and As
it seems to me they have the same pronuntation when i heard it . What do you think?
In Brazilian portuguese they have the same pronounciation, but not in European portuguese. 'as' sounds like the english pronoun 'us', and 'às' is more opened like the 'a' in father. But even brazilians don't know when to use them beacause they have the same pronunciation and some think is useless to try to distinguish them graphically.
"às" is used when you want to put an article before the noun with the preposition "a". Example: "I give the letter to the girls" is translated as "Eu dou a carta às meninas".
If you are not sure which one to use, change "a" to "para" and you will get the correct sentence: "Eu dou a carta para as meninas".
So "a + as" = "às". Similarly "a (to) + a (the 'feminine') = à". In the masculine case there's no confusion: "a + os" = "aos" and "a + o" = "ao".
When you forget to use the grave accent, you may cause some ambiguities, for example: (wrong!) "eu denuncio a menina a mãe" could mean (1) "I denounce the girl to the mother" or (2) "I denounce the mother to the girl". In the right form it should be (1) "eu denuncio a menina à mãe" e (2) "eu denuncio à menina a mãe".
Notice that portuguese allows many different constructions and orderings. That's one of the richness of our language (and one of the annoyances when writing technical texts).