uses
  ZConnection, ZDataset;

var
  Conn: TZConnection;
  Query: TZQuery;
begin
  Conn := TZConnection.Create(nil);
  Conn.Protocol := 'postgresql';
  Conn.HostName := 'localhost';
  Conn.Database := 'mi_basedatos';
  Conn.User := 'usuario';
  Conn.Password := 'contraseña';
  Conn.Connect;

  Query := TZQuery.Create(nil);
  Query.Connection := Conn;
  Query.SQL.Text := 'SELECT * FROM tabla;';
  Query.Open;

  while not Query.EOF do
  begin
    writeln(Query.FieldByName('campo').AsString);
    Query.Next;
  end;

  Query.Close;
  Conn.Disconnect;
end.