# $j$-$j$ coupling interaction in Magnetic Resonance Spectroscopy

I am studying Magnetic Resonance Spectroscopy and I have some difficulties in understanding the j-j coupling interaction. What does actually happen from the physical point of view to the electronic cloud of the neighbouring atom? When I try to understand in books like A Complete Introduction to MODERN NMR Spctroscopy of Roger S. Macomber (but also in websites) it seems to me that there are explainations more focused on quantum theory and its rules, but what I want to know is simply what happens physically at the electronic cloud and the consequent interactions ? Therefore why does this causes that in the spectrum, for example, of the Ethanol molecule (CH3CH2OH) there are three peaks related to -CH3 group? Or why in the Acetaldehyde molecule (CH3COH) there are four peaks related to -COH group and two peaks related to -CH3 group just for the j-j coupling interaction?

I really would like to see things clearer at the basis (so what happens physically to the electronic cloud and the consequent interactions) and thus being able to understand the number of peaks (while I think I have understood the chemical-shift interaction).