How to add noise

Hi this is my voxel engine so far…

This is my chunk class - http://pastebin.com/W64LSh07
This is my main game class - http://pastebin.com/axULjzRt

Could someone please tell me how to add random noise to this engine, so my voxels have different heights thus making random generation, I have looked a simplex noise i just dont know how to add it to my engine

Thanks Toby