If it goes over your head it is because materials have complex behaviour, so we have invented all manner of simplifying assumptions to put the common materials in neat and tidy classes which each follow neat and tidy types of behaviour. So you end up with a colossal mess of stuff to memorize and get your head around.
The mathematics which governs the universal behaviour of all materials is beautiful, elegant and makes perfect sense. It's just not amenable to engineering calculations so they will never mention that.