The following diacritics are used in Portuguese:

• acento agudo (acute accent);

•  acento grave (grave accent);

•  acento circunflexo (circumflex accent);

•   til (tilde);

•  cedilha  (cedilla);

• trema (dieresis);

• apóstrofo (apostrophe).

I suggest you read the pages Alphabet & sounds, Consonant sounds & spelling and Vowel sounds & spelling before studying the accent rules.

View also Rules of accentuation.

• The acento agudo can be placed above vowels, e.g: árbitro (referee, arbitrator), época (epoch), índio (Indian), óbito (death), úvula (uvula);

• The acento grave can only be placed above vowel a to indicate crasis (vowel merger), e.g.: àquela (for that, to that);

• The acento circunflexo can only be placed above vowels a, e and o, e.g.: âmbito (range), êxodo (exodus), ômega (omega);

• The til can only be placed above vowels a and o, e.g.: nação (nation), nações (nations);

• The cedilha can only be placed below consonant c, e.g: cação (dogfish);

• The trema can only be used above consonant u, e.g: qüinqüênio (quinquennium).

• Words cannot begin with ã;

• Words cannot begin with õ or end in it;

• Words cannot end in â;

• Words cannot begin with c-cedilha (ç);

• Words cannot begin with ü or end in it;

• Words cannot end in à.