Note: I have never watched Avatar or Legend of Korra. I don't know how similar this idea is to that universe.
Suppose that we can manipulate air, water, earth, and fire. To an extent. Most (but not all) people are born with the ability to manipulate one of the four classical elements. Using it for non-trivial things requires training and discipline, and is analogous to exercise and physical training as we know it. Your Average Hydro Joe couldn't channel groundwater into a geyser, but he could probably spray water at someone who tells a really bad joke.
More specifically, let's assume the following:
- The universe is still made of protons, neutrons, electrons, and their 118+ interesting combinations.
- It's still the same planet Earth we know and love.
- Humanity's biological history up to the point of the emergence of Element-Making powers is much the same.
- Even though I may use it for analogies, I'm not assuming that science, nations, etc. develop as they did in reality.
- "Earth" refers to most forms of inorganic matter.
- "Fire" refers to heat and combustion.
- "Water" refers to...water. H2O. This includes ice, snow, and humidity (but liquid water is easiest to Make).
- "Air" refers to gasses and their motion.
- Element Making is hereditary in nature, and cannot be learned if you don't have the natural aptitude (Joe Hydro can't manipulate fire, for example).
- You can be a carrier. Joe Hydro may be a water Maker, but he may be carrying a fire Maker gene. If he has a kid with a fire Maker, the kid is fairly likely to be a fire Maker him/herself. If he has a kid with an air Maker with a fire Maker gene, the kid could still be born a fire Maker, but it's not likely.
- Some people can Make more than one Element. The prevalence of double-Element Makers is on par with that of certain other uncommon traits such as red hair, ambidexterity, or double-jointedness.
- If you can't Make any Element, you're probably in a support group.
- If you can Make two Elements, you're probably popular at parties.
- If you can Make three Elements, you probably have a Wikipedia page about you.
- If you can Make all four Elements, you probably have a religion named after you.
- Element powers are evenly distributed, by number, across the human race. However, some ethnicities or cultures are more propense to certain Elements than others (for example, maybe Asians are more likely to be Earth-Makers, Africans are more likely to be Fire-Makers, and Europeans are split between Water and Fire).
- You cannot tell just by looking at someone what they can Make (modulo the usual ethnicity distributions).
- Like physical strength, everyone's limits varies on an individual basis. But your Making skills can be honed just like your biceps can; by pushing them to their limits regularly, in a manner analogous to working out at the gym (but with more of a mental component).
- Temporary performance boosters analogous to steroids exist, and they do indeed affect you negatively if you abuse them.
- Higher skill in Element-Making usually involves more efficient energy expenditure, greater precision, and wider ranges.
- Staying healthy (eating your vegetables, getting enough sleep, not being depressed, etc.) can help you be a better Maker.
- When you use your powers enough, you get really tired, and might even collapse. This is also true of running a marathon.
- You can't create the Elements, you need them to be nearby. An astronaut on a spacewalk isn't going to be doing much Air-Making, for instance.
Infrequent or Unskilled Makers
Usually these are children, or people with both physical and mental handicaps.
Air: Can blow out birthday candles.
Water: Can stir around water in a container (e.g. when making pasta).
Fire: Can light candles or cigarettes at close range.
Earth: Can mix the dirt in a potted plant or knock down a sand castle.
Someone whose day job doesn't involve Making, or someone still in training like a college student.
Air: Can redirect smoke that's blowing in their face.
Water: Surprise water-balloon fight!
Fire: Can light a campfire or keep a pan hot long enough to cook a meal.
Earth: Can dig a hole.
Someone whose career revolves around some application or study of Making. They've been at it for probably eight to ten years.
Air: Can delicately guide a paper airplane in detailed paths.
Water: Doesn't need an umbrella, can redirect nearby rain to fall around them.
Earth: Can sculpt stone into a statue.
When these Makers say something, people listen. Probably twenty-five to thirty years of professional experience. These are the John Carmacks or Neil deGrasse Tysons of Making. They might even have a verified Twitter account if they're trendy enough.
Air: Can fly.
Water: Portable water cutter.
Fire: Can melt metals and rocks without getting the surrounding area hot.
Earth: Can disintegrate a boulder into sand.
In the History Books (comparable to Einstein, Newton, etc.)
Talent like this comes around maybe once every few hundred years. Comparable in skill and influence to Plato, Einstein, or Shakespeare. These people have words named after them.
Air: Can incite tornadoes.
Water: Can manipulate the weather if the clouds are already present
Fire: Can burn down a forest during a downpour.
Earth: Can incite earthquakes.
How could such a society have evolved, starting from about 2000 BC to the modern day? How would law and culture develop, and how would they differ from our own?