Magic & Aura

Overview
To understand what magic and aura are, you need to know what they represent. Magic is the representation and expression of one's mana, while aura is the expression of one's will. While they both do wildly different things at their core, they are two sides of the same coin.
Magic
Before we talk about magic, one must explain the concept of mana. Mana is the basis of all magic. It also exists in all living beings and some inanimate objects, but that's a topic for another time. It's common for people to use mana without noticing to perform particular actions. For example, a dragon using their breath weapon or a kitsune making an illusion. These abilities cost mana, but it wouldn't be magic. In some cases, stamina can act as a replacement, but that's a case-by-case basis.
Magic is what happens when someone causes a change in their mana and converts it. Think of turning your mana into fire or lightning, for instance. This type of magic also allows you to control already existing elements, which costs less than making it directly from your mana. Although, like most things, you won't immediately be able to control every aspect of your magic without proper training.
As you expect, some people are better at controlling their magic than others. Some are born with more magic potential, while others spend years studying the arcane arts. There's also the chance of getting lucky and randomly gaining magic. It depends on the situation.
Aura
In comparison, aura is a lot simpler. As stated, aura is the expression of one's will. While all living beings can have an aura, if they're weak-willed, it would be impossible to use their aura effectively. You would commonly see more humanoid creatures using an aura than an animal.
Aura's primary purpose is reinforcement and strengthening. When someone first manifests their aura, it will surround their body. It will act as a protective shell around the person, and they will be able to increase their damage output. It's also possible to shape and detach aura from the body, but that takes practice. Just like with magic, it can interact with the elements too. When properly combined, the properties of the aura get changed, and a degree of physicality becomes apparent.
Some are naturally better at controlling their aura than others. But it is more cut and dry. If you have a weak will, it will be harder to use, and if someone causes a negative change within you, it could mess with the usage. However, if someone perseveres and grows from the experience, it could grow in power.

Manifestation

Magic can manifest itself in a variety of ways. Some people use magic to conjure the elements, enchant objects, or do supportive things. The source of someone's magic also varies. Some people study, others pray to gods, some make deals, while some are lucky. Because of these factors, the magic people cast ends up being unpredictable.
Aura starts simple, colorless energy surrounding the body that buffs. However, with practice and development, particular objects become easier to create, and certain items become easier to cover. For example, an army commander's aura could buff and boost the morale of his troops, and he may have an easier time creating a flag.

Localization

As previously stated, mana and aura are everywhere. It takes practice to use them and to understand them. In developed communities, it's common to see those magic. Aura is a little rarer since it takes a strong will, and some have found it easier to use their mana instead.

Side Information
Now you might think magic and aura are pretty cool and think about using both. Now I want you to throw that idea into the trash. You don't see a pugilist casting a giant ritual or archmages using their aura to punch people. But for an actual reason, the body can not handle using both forces together. Using them can cause damage to the body that takes a long time to heal. In very few circumstances can someone wield the power of aura and magic together. But it's safer to learn how to use one.

Type

Natural