Volume control option...

I am working on a demo game project, in my game i want to use option screen which contains volume control, mute volume and toggle full screen.

i have done mute volume and toggle full screen, but how to create volume control option?


Here is the link for one
http://tdn.garagegames.com/wiki/Torque_2D/StandardTutorials/Basics/GuiScene

but i cant understand this one...

anyone help?

Thanks.