There are four main elements, a couple other important ones others call polarities, sub-elements (results of elements being mixed), and other "lesser" elements, for lack of a proper term. The interpretation of what each element is a symbol of is up to the user though.
Four Main[]
Think of the elements and what they're used for. They all have their uses in magick too. None of them have a specific universal role.
Fire[]
Fire is what keeps us warm here, and is also what helped us lead to civilization. So it is like a representation of willpower to some people.
Water[]
Water is one of the most important things in staying alive. So according to some people it is a healing energy.
Earth[]
People tend to associate it with grounding, but who said you have to go with the majority? Stone and wood are what we make shelter out of, so Earth is like endurance to some.
Air[]
We need Oxygen to breath, and wind is also something that represents intelligence to some people, because while Earth is stable, the Wind travels everywhere, and people that travel learn new things, and understand, which shows intelligence.
"Polarities"[]
Keep in mind when reading these that none of these are evil or good, even if there was such a thing these wouldn't be representations either.
Light[]
It tends to be associated with certain "divine" qualities, but can exist in beings that don't have a divine source.
Dark[]
It tends to be associated with shadows and such beings, and can exist in other beings too.
Chaos/Void[]
It is where everything is said to come from and is also known as a perfect balance between all the elements.
Other Elements[]
Some of these are also said to be a part of chaos.
Time[]
Time as an affinity deals with ones perception of time but there are beings that have it are able to manipulate time in a fashion that it affects a particular area around them.
Cosmic[]
Cosmic affinity is associated with stars, planets, cosmic dust and such beings.
Solar[]
Deals with internal or external manipulation of energy that is said to be from the sun and works with light energy.
Lunar[]
Deals with internal or external manipulation of energy that is said to be from the moon, is also associated with shadows and works with dark energy.
Electricity[]
Basically like the electricity we use, and I'm unsure of it's uses at the time, but I know that you can get it from electrical devices here, I think. (Will edit more when I experiment with it.)
Sub-elements[]
These elements are elements that are the result of mixing other elements.
Ice[]
The result of mixing (cold) air and water.
Lava[]
The result of mixing earth and fire.
Steam[]
(The amount who believe this is an affinity is smaller than others). The result of fire and water.