On the topic of magic systems: my own take on magic

I guess a good place to start would be Splintershard's more primitive version of this magic system.

In Splintershard, magic is driven primarily by intent and willpower, with some amount of vague "mana" being thrown around as an expendable source of energy that replenishes itself with time.

There isn't all too much beyond these rudimentary guidelines, aside from the usual blerbs about practice leading to improvement
there are enchanted items, and crystals can be used to store certain spells and/or raw mana, but the mechanism behind how that works was never explored beyond "too much mana in one place = boom", as well as a not-really-all-that-well defined split between "normal" magic and "harmony" magic since the story takes place in Equestria. Chaos magic is grouped in with harmony magic.

The system of "magic" that I'm working on defining in my Fractures story relies primarily on two central aspects: intent/willpower, and raw energy.

Spells are nothing but an extension of the caster's intent, and draw upon the raw energy of mana to do their work.
Beginning with the energy aspect, mana is a naturally-occurring substance that normally exists in either liquid or gaseous state, and is a biological product produced passively by many living organisms.

It is similar in biological function to ATP in our own bodies, being a sort of intermediary form of energy storage that is used shortly after being created in whatever task requires it.

The major difference, however, is that mana is far denser than ATP in regards to stored energy, and can be likened more to almost a sort of biological "radiation", similar to that of radioactive materials in real life, but minus the hazards of such.

Creatures capable of casting magic utilize mana in a far different way than those that aren't capable. It is produced within the bodies of these creatures, and exists in a highly dilute form in normal circumstances. When spellcraft is initiated, a rush of mana distills itself from the solution, traveling along to the site of intended concentration, which normally will be located on the extremities of one's body.

It is here where the explainable halts and the not-so-explainable begins instead.

Here, the mana is able to "couple" for lack of a better term, with the will of the caster. Mana naturally follows the strongests of wills and intents, but in this form has a very short range, and so despite being possible, it tends to be very hard, and largely unheard of, to even be able to possess someone else via magical means. Looking past the potential to force one's will upon others using magic, mana is now used as a stream of raw energy to be drawn upon by the caster.

Moving objects via telekinesis, for example, will draw differing amounts of mana depending on the force required to achieve initial movement or balance out an opposing force.

Fabricating items is possible with the transformation of energy into matter, but the ridiculous amounts of mana needed for such a spell makes it unfeasible to most, if not all.

Because of its biological nature, mana can often easily be replenished by eating food, as, not only does one's body convert some of the calories consumed into mana stores, but traces of mana remaining within food will also be accepted into one's body. This aspect results in the ability to farm raw mana en-masse.

However, concentrated mana is highly unstable, to the point of being quite explosive. This reactive nature of concentrated mana will lead to chemical burns for those who come in direct contact with the liquid and gaseous forms. As a result, concentrated mana is typically reserved only for industrial or military operations, though small amounts of it can still be purchased in specialty shops for various purposes.

Moving onto enchantments now.

Enchantments are a sort of "container" for spells and/or mana. In a way, the reinforced flasks that concentrated mana is packaged in is a type of enchantment because of this classification.

Enchanting items is a lengthy and mentally-tolling process. The process of enchantment, similarly to simply casting the intended spell manually, relies heavily on willpower, but also draws on an additional dependency--experience. Magical prowess grows naturally with experience as mental pathways open, providing more efficient ways for mana to be utilized in a spell. During the process of enchantment, a special spell is used that quite literally transfers that knowledge and experience into the item intended to be enchanted, meaning that the cost of enchantment is one's knowledge and experience of the original spell.

This greatly restricts the number of enchanted items that exists, especially ones containing powerful spells.

Nobody wants to have to re-train after dumping their experience into an inanimate object. As a result, enchantments tend to instead be lower spells, mostly; Things such as light and heat, which, in the form of spells, are some of the simplest to re-learn, as they are in effect simply a way to directly expel mana from one's body with a degree of regulation.

As a result of this simplicity, flashlights, small heaters, etc. are often either electricity or magic-based, depending on what energy source is more readily available.

Enchanted items will normally draw on their user's mana stores, as they serve as an extension of their wielder's will. However, it is possible to, and at times even required, to "feed" enchanted items with mana. This mostly involves soaking the item in a vat of dilute mana in either liquid or gas form, though the former tends to be faster, albeit more often than not uneven in distribution across the item.
Alternatively, another way to "feed" enchanted items, which, in this case, instead strengthens their bond with their user, is to dissolve some biological substance from said user (hair, nail clippings, etc.) within a neutral compound, and soaking the item within said compound.

This form of feeding is referred to as "sacrifice", due to how the enchantment in a way "consumes" a part of the user.
Alternatively, a more natural method to go about this bond-strengthening is to simply use the item more, and with direct skin contact,
Skin oils and dead cells are consumed by the item in the same way the "sacrifice" method of feeding happens, and though they are ultimately converted with time into mana held deep within the enchanted item, they also leave an "imprint" of the user on the enchantment itself, separate from the item, that not only strengthens the bond mentioned earlier, but also can be used as a form of identification, or even security if the bond is strong enough.

Amulets are a special type of enchanted item that often contain dedicated mana stores of their own, and are thus able to operate independently of their owners once the intent to cast the spell is given. This dedicated mana store means that they almost universally require recharging with concentrated mana, or else they require hours of physical contact with their owners to naturally recharge.

However, it also means that, aside from the bottles and flasks of raw mana, enchanted amulets are also one of the most volatile items purchasable in the consumer space, right up with explosives such as fireworks. Regulations exist to keep them to some standard of quality, as defects such as cracks and fissures can lead to leakage of mana, which is not only a biohazard, but also risks explosion.

As for portals, they're basically like black holes, but without the succ. One-way travel only, with limited special exceptions (light-speed objects, mostly.)