World Generation questions

I'm curious as to how world generation works. Specifically the default world generation within the ChunkProviderGenerate. Most(if not all) of the variables within the code is generically named(i.e. var1, var2, var3) rather than being named by what the variable contains. Can anyone break down how the noise generation works?

If someone could just explain what all the variables are for and how they work within the algorithm I'm sure I could figure out the rest by myself.

Thanks,

CubeArchon