How do GUI Sliders work

how does a GUI slider work? i tried this:

var Number = 10;
function OnGUI () {
Number = GUI.VerticalSlider(Rect(10,10,40,200),Number,20,0);

but it wouldnt work, any reason why?

(in otherswords, how do you use a GUI slider, noob question i know but i cant find it ANYWHERE, and yes i did read the wiki and the runtime class available on resources)

"Number" is a particular system type, and you can't use it as a variable name. This is one of several reasons why it's a good idea to always use lowercase for variable names.

I think "Number" is JavaScript type. Try renaming "Number" to something else, like "number".