PostgreSql-users and passwords

I'm bening to work with Java an PostgreSql. When i try to access a
database which is on the server using
DriverManager.getConnection("jdbc:postgresql://host:port/banco","user",
"password"); an error occurs:"User authentication failed". Where do i
configure users and passwords for my database in the Postgresql?

Can anyone help me?
Thanks,
Elaine Araujo.
ps. The application is on a cliente.