The term on its own is most often used to indicate the presence of arcane energy, magic is actually a rather broad category, all at once defining both the means by which an individual can channel abilities beyond mundane capabilities as well as being an umbrella term that encompasses (sometimes incorrectly) the categories of such channeling. In short, magic entails the drawing upon and manipulation of vast powers, be they a manipulation of the arcane that permeates the world around us, being bestowed divine gifts through prayer to deities, or though other means altogether.
Mana is a very theoretical term used mostly by those that study the relationship between such powers and how they interact with the physical form of the caster. In this regard, 'mana' represents an energy reserve much like any other that the body might harbor and dictates how much of an external power a body can channel before risking exhaustion, injury or being overwhelmed by that source.
It is well documented that practice in channeling, much like practice at swordplay or archery, will exercise the capabilities of the caster and will over time increase how much power they can draw. The amount of mana the body can store causes no physical change to the caster, but casters are very aware of their limitations. As they begin to exhaust their mana reserves, or 'mana pool', they will begin to feel nauseous and tired. To be completely drained of one's mana can exhibit symptoms such as trembling and a temperature, which can go on to manifesting as a full-blown sweating sickness if repeated too often.
Foci, Instruments and Ritual
Mana, much like most of the magics that utilise it, hold no physical form. No physical or alchemical stimuli seems to alter the means in which one interacts with their mana other than foci. Foci are items imbued with residual magic and somehow attuned to the individual that seems to allow the energies channeled to flow easier and safer through the body, essentially acting as a safety-net for the caster to assure that they do not cause themselves any harm whilst hastening their spell. They are rare in Ereda because in that they cannot be produced artificially or en mass, but have to be catered to the individual. Foci crafters will generally require an item with sentimentality and purpose of an item in order to easier attune it to being a focus. The crafting of foci is an an undisciplined art that has no real right or wrong method behind it, just patience and understanding of the arcane, and takes a lifetime to master. Most arcanists that are able to create foci come from families where these methods have been passed down from generation to generation.
Whilst there is no artificial stimuli that will improve the reserves of mana, there are schools of magic within the arcane that utilise an instrument through which a caster can channel. Wand magic, staff magic and runic magic are three examples of such casting. These disciplines teach the arcanist means of channeling magic using something other than themselves as a conduit, be it the staff they weild, the wand they point, or the rune that they draw. The items themselves are not inherently magical - a wand-wielder can pick up another wand and still be able to cast a spell - but over time such an instrument will have residual energy from that same caster.
Within the arcane, rituals are a practice of empowering and enacting a spell beyond the capabilities of a caster that involve a great deal of preparation and calculation in order to be pulled off correctly. Traditionally involving a circle of some description, rituals are a notoriously risky practice. The components of a ritual need to be meticulously chosen and placed in order to ensure that the power being drawn in can be evenly distributed, lest it will be unfettered and potentially disastrous and dangerous to those involved. Divine rituals are much easier in this regard, as the divine cannot cannot be inconstantly tapped into. Other than clarity of thought through prayer, however, there are very few accounts of divine 'rituals' working and the authenticity of those accounts are quite often arguable. A ritual of exorcism is an example of a ritual that will most likely see the gods bestowing their power unto the caster. It is in the interests of the divine that the diabolic be cast back into hell.
The examples of rituals that can be relied upon, taught, and reproduced without the same level of caution come in very specific schools of magic. Runecasting is one such example, which simply requires a ring of runes in a certain sequence in order to make impenetrable barriers, amongst over things. This is due to the specificity and dedication that such a school requires, as imbuing runes with power is no easy discipline to learn. Diabolism and druidism both see rituals in their practices, but the dark arts of summoning demons and the taboo arts connected to the Fringe are made all the more dangerous for just this reason. Such power, whilst easier to wield in such quantities, comes at a steep price, be it exposure to the twisting effects of the Fringe or the damnation of one's soul.
Magic, Alchemy and Technology
The relationship between the arcane and the alchemical is one that doesn't quite match up. Whilst there are potions in the world that can seem to possess magical properties, such as the capacity to cause someone to turn invisible, the potion itself is not magical. The components that go in it might be kinds of plants that grow in sites of potent magical activity (see: leylines), but even common plants have the potential to, in the right quantities, grant those that imbibe them the capacity to see in the dark or to bestow them with temporary strength. Attempts to invigorate the alchemical with the magical have been unanimously recorded throughout history as catastrophic and impossible. Even the reverse is true - there are no concoctions that an alchemist can brew that might increase the body's mana capacity or replenish what has been spent.
It is seldom that magic and machine have been successfully implemented together, likely as a result of the prevalent mentality that magic of all kinds is a form of power that should not be tampered with outside of its own field. It took the rare kind of genius that boardered on insanity to develop a field of magic that incorporated machinery within it.
Any spells that are drawn from the world's magical essence without any external mediation is an arcane spell. The casting of such a spell is usually induced by the utilisation of at least a verbal or somatic componant and otherwise relies only on the mage's mana reserves. Sometimes a mage will require additional components, such as a weapon or a reflective surface.
There is no one way to teach a mage their spells. Across the Realms budding mages have been historically taught their craft in various different ways. Calavrian arcane studies and traditions are by far the most steeped in tradition and knowledge. It is from Calavria that the image of a mage and his book of spells comes from, as Calavrian mages wrote countless tomes on the subject of the arcane as they tried to better understand the power they weilded. In contrast, the Norlish mages surround their use of the arcane with symbolism surrounding their ancestors. In their incantations they ask their ancestors to grant them their spellcraft, believing that heroes of their bloodlines linger in the world influencing the flow of the arcane. To the Norls, the vocal and somatic componants exist to attract the attention of their ancestors to them.
As wll as the capacity to shape, identify and manipulate raw arcane power, arcanists have the capacity to learn how to manipulate the elements, how to prophecise the future and how to create illusionary images.