System Packages Oracle PLSQL

SQL>
SQL> set serveroutput on
SQL>  begin
  2        dbms_output.put_line( 'One' );
  3        dbms_output.put_line( 'Two' );
  4        dbms_output.enable;
  5        dbms_output.put_line( 'Three' );
  6      end;
  7      /
One
Two
Three
PL/SQL procedure successfully completed.
SQL> --