Why Doesn't This Work?

I recently downloaded the procedural unity example project and came across something that I can't figure out. In one of their script theirs these lines:

 private var perlin : Perlin;
 private var fractal : FractalNoise;

I made them public but nothing showed up in the inspector. If you can't assign something to it then whats the point of having it? What do these lines mean because I though you could only make variables ints, floats, booleans, ect... Then I put these lines of code in a new script and I got the error: The name 'Perlin' does not denote a valid type ('not found'). Did you mean 'TreeEditor.Perlin'? and The name 'FractalNoise' does not denote a valid type ('not found'). Did you mean 'TreeEditor.FractalNoise'?

Here is the whole script from the example project in case you need more info.

 // This script is placed in public domain. The author takes no responsibility for any possible harm.
 
 var gray = true;
 var width = 128;
 var height = 128;
 
 var lacunarity = 6.18;
 var h = 0.69;
 var octaves = 8.379;
 var offset = 0.75;
 var scale = 0.09;
 
 var offsetPos = 0.0;
 
 private var texture : Texture2D;
 private var perlin : Perlin;
 private var fractal : FractalNoise;
 
 function Start ()
 {
     texture = new Texture2D(width, height, TextureFormat.RGB24, false);
     renderer.material.mainTexture = texture;
 }
 
 function Update()
 {
     Calculate();
 }
 
 function Calculate()
 {
     if (perlin == null)
         perlin = new Perlin();
     fractal = new FractalNoise(h, lacunarity, octaves, perlin);
     
     for (var y = 0;y<height;y++)
     {
         for (var x = 0;x<width;x++)
         {
             if (gray)
             {
                 var value = fractal.HybridMultifractal(x*scale + Time.time, y * scale + Time.time, offset);
                 texture.SetPixel(x, y, Color (value, value, value, value));
             }
             else
             {
                 offsetPos = Time.time;
                 var valuex = fractal.HybridMultifractal(x*scale + offsetPos * 0.6, y*scale + offsetPos * 0.6, offset);
                 var valuey = fractal.HybridMultifractal(x*scale + 161.7 + offsetPos * 0.2, y*scale + 161.7 + offsetPos * 0.3, offset);
                 var valuez = fractal.HybridMultifractal(x*scale + 591.1 + offsetPos, y*scale + 591.1 + offsetPos * 0.1, offset);
                 texture.SetPixel(x, y, Color (valuex, valuey, valuez, 1));
             }
         }    
     }
     
     texture.Apply();
 }

Also that script contains the line:

 var valuex = fractal.HybridMultifractal(...);

If you search for this function you get nothing. This really stumps me because you can't just make up functions! It cant be a .Net method because nothing is being imported.

Please help me under stand why there are made up functions and variables of type "Perlin" and "FractalNoise".