Elements have been a fantastic way to organize magic systems for ages, right? For explaining powers linked to earth, air, fire, and water specifically, I’d look for books where the elemental structure is hard-coded into the worldbuilding. Something like the 'Avatar: The Last Airbender' novels, obviously, which are direct expansions of that universe. Then there's Tamora Pierce's 'Circle of Magic' quartet—each book focuses on a young mage mastering one of those four elements, and it’s woven into their personalities and the plot's conflicts in a really grounded way.
I also think of 'Uprooted' by Naomi Novik, though it’s not a strict quartet; the antagonist's magic feels deeply tied to a corrupted forest, which is an earth-adjacent power. For a more philosophical take, the classic Earthsea books by Ursula K. Le Guin treat magic as a language of true names, but the equilibrium of the world is based on balancing these fundamental forces. The way she writes about sailing and the sea is practically a treatise on water magic itself. Those would be my top picks for clear, explanatory systems.
I'm probably forgetting a ton of indie fantasy that does this, honestly. There's a whole subgenre.