Nana_Brazil

:brazil

DE = CAN BE: FROM, OF, BY.
When we use as FROM just take a look at how to do it:

DE = FROM
DE + O = DO FROM ( MALE -THE)
DE + A = DA FROM (FEMALE - THE)
DE + OS = DOS FROM (THE -MALE - PLURAL)
DE + AS -= DAS FROM (THE - FEMALE - PLURAL )
As in English we say "I am from Brazil "- because THE is not used before a proper name, it causes mistakes when speaking Portuguese, which is used in sentences. Let`s see some examples:

I AM FROM BRAZIL - EU SOU DO BRAZIL . (do = de + o)
I AM FROM RIO - EU SOU DO RIO

BUT - I AM FROM SÃO PAULO = EU SOU DE SÃO PAULO. - (maybe because it refers to a saint proper name).

SHE IS FROM FRANCE - ELA É DA FRANÇA
HE IS FROM THE USA. - ELE É DOS ESTADOS UNIDOS.

The same occurs with names.

I am a friend of João.( or I am John`s friend) = Sou amiga do João.

I am a friend of Maria. = Sou amiga da Maria.