Each element exists in a group and there are just over 20 groups.
You start with 4 groups since you have the 4 basic elements: Air, Fire, Water, Earth.
As you combine elements you'll eventually unlock more groups. Here's the remaining ones and an example of how to get them in no particular order:
Animals - Example: Air + Egg = Bird
Energy - Example - Air + Fire = Energy
Humans - Example: Golem + Life = Human
Materials - Example: Clay + Fire = Bricks
Organisms - Example: Life + Swamp = Bacteria
Plants - Example: Earth + Moss = Plant
Resources - Example: Domestic Animal + Human = Wool (and meat and blood)
Supernatural - Example: Ash + Life = Ghost
Tools - Example: Human + Metal = Tools
Transportation - Example: Wheel + Wheel = Transportation
There are other groups in the other episodes as well. These are just the basic ones.