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If you were born in Brazil, you are a Brazilian citizen by birth. That is true whatever your parents' nationality, and it stays true however long you have lived elsewhere — the only exception is a child born to parents who were in Brazil in the service of a foreign state, such as posted diplomats.
So there is nothing for you to claim. What you are missing is documents, and the order is fixed: first a current copy of your Brazilian birth certificate (certidão de nascimento) from the registry office that recorded the birth, then a CPF number, then a passport at a consulate. If you do not know which registry holds your birth record, the consulate covering where you live can search for it.
Tell us where you were born and where you live now, and we will find the registry and work out what has to be requested first.