Single Slider gives you a graphical presentation for a unit of measurement picker. The user can pick a number based on the slider location. After this number is picked, triggers can perform an action.

Dual Slider gives you a graphical presentation for a range. The user can pick a range out of a larger range e.g. the range of digital cameras price is $100 - $1000 and the user wants to see the ones between $200 - $400.