SQL & PL/SQL

What is the preferred way of creating stored procedures? Can I use SQL Developer or SQLPlus?
I'm running version 11.2.0.1.0.

Here is my attempt in SQLDeveloper:

CREATE OR REPLACE PROCEDURE hello ()
BEGIN
dbms_output.put_line('Hello, World!');
END;

SET SERVEROUTPUT ON;
SELECT hello() from DUAL;

When I hit F5 it says

Warning: execution completed with warning
PROCEDURE hello Compiled.


When I select the last line and hit F9 I get a dialog box that says:

An error was encountered performing the requested operation:

ORA-00904: "HELLO" invalid identifier
00904.0000 - "%s: invalid identifier"
*Cause:
*Action:
Vendor code 904 Error at line:8 column 7

I tried using SQL plus but since I'm having trouble just logging in, I already posted my query in the SQLPlus forum.

Thanks,
siegfried