Create joomla module with parameters

I'm new to joomla 2.5 and I was looking at joomla tutorials on how we can create modules, but there's nothing about how can we add parameters to it. What I did for now is that I created a module that display a hello world message to my page and now I want to have a parameter in my module with a label your message. This way, the administrator will set the new message and I can return it using the helper.php file.