The elements are the things that make up the universe as we understand it. I think how different people understand and interpret the elements can vary, so I don't think it's particularly strange that different people "use" different elemental systems. For myself, I use a five element system that's something of a hybrid between eastern and western systems: earth, fire, air, water and metal.
Based on a series of dreams I had when I was eleven or so, I have held that Fire was the first element to manifest, followed by Water, Earth, Air, and finally Metal.
Each element pairs with an aspect. Aspect is not actually a very good word; functionally, light and dark, chaos and order and (void) are essentially also elements. But I started using the word when I was a preteen and it's stuck.
This is one of those areas where my work is intensely personal, not because it's private but because I'm not sure it's meaningful to anyone who's not me or practicing with me. I don't think the elements as I understand them are a universal truth - lots of people separate earth and wood, for example, but that's simply not how it works for me in this system.
I don't talk about this often, because... well, who dreams of a religion when they're eleven and spends two thirds of their life trying to figure out what that religion is? Or, as I'm doing now, reconstructing it. Because I never did find something that fit precisely, without me having to snip off some heels and toes.
The first dream I had was actually Earth's dream, but inside the dream I knew that Fire and Water were there because they had already manifested. Air came later, and Metal was the last piece of the puzzle. This was where I learned that the world ends, and life goes on, over and over again. Each element, fully manifested, can change the world and break it. There are little apocalypses and there are big ones but always someone picks up the pieces.