Those questions are better answered by doing the individual research for yourself, as you can retain more through experience and understanding.
In short, the macro tiling is multiplying any number of combined alpha textures (black and white) by the base/diffuse color. This, in turn, creates that patchy and seemingly randomized look to the landscape. What it is actually doing, is breaking up the visible tiling of your repeating textures by adding variation at different scales overtop of one another.
To parameterize the macro tiling and to better understand how it works, you can add a single scalar parameter to the multiply of the TexCoord node as shown below.
Macro Variation Parameters
If you are still having difficulties understanding these concepts, you might want to go back and make sure you have a grasp on how textures work within materials, and basic UV space information.
[Textures - Documentation][2]
Thanks,