How do I make a Scale GUI were if you move the arrow thingy the size changes?

Sorry if this doesn't make too much sense, and sorry if I'm asking way too much I'm just really stuck and don't know how to even make gui scales, let alone having it change your size. I'm still learning so even just a tip would help me... Thanks ^^

local Size = 2.0
local Humanoid = Character.Humanoid

Humanoid.HeadScale.Value = Size
Humanoid.BodyHeightScale.Value = Size
Humanoid.BodyWidthScale.Value = Size
Humanoid.BodyDepthScale.Value = Size

end)
end)