How to make PHP widget .

[K a M a L]

Hello ,
I want to ask what is the proper way to create a PHP widget in Vbulletin 5 .
I'm not able to output anything in the widget
I tried

PHP Code:

echo 'test'; 


and

PHP Code:

 return 'test'; 


and

PHP Code:

$output= 'test'; 


but didn't get any output in all cases .. Also I want to ask where is widget is processed and what is the variable scope available there ..
Thank you!