You may change the gender of many nouns by:

1.  Changing the final vowel to make a masculine noun feminine:
filho (m) (son) / filha (f) (daughter)

2.  Adding a to the masculine noun:
cantor (m) = singer / cantora (f) = singer

3.  Dropping the final vowel and adding a suffix:
poeta = poet (m) / poetisa = poetess (f)

4.  Changing the article preceding the noun (many nouns can be both masculine and feminine):
o estudante (m) = the student / a estudante (f) = the student