Use a narrative citation when the author's name is part of your sentence:
Nadeau (2012) stated that chocolate is delicious.
According to Nadeau (2012), chocolate is delicious.
Use a parenthetical citation to cite information that does not belong in the sentence grammatically:
Chocolate is, in fact, delicious (Nadeau, 2012).
As one author argued, "chocolate is delicious" (Nadeau, 2012, p. 1).