[@The Fox Without] Items are enchanted in a variety of ways. For the most part, spells are imbued onto materials through patterns, such as runes carved onto a piece of wood or metal- or even the an adornment, such as the gold wrapping around a bauble. Weaker enchantments, such as making the object warm to the touch, or glow, is pretty much self powered, and can power itself indefinitely without the enchanter having to waste mental resources on it. On the other hand, more powerful spells, such as dulling the force of a blow upon impact or setting a weapon ablaze requires considerably more energy- though this energy is generally provided by the wielder as opposed to an enchanter. 

A very common enchant is to turn gems and precious metals into 'magic' reservoirs. In this world, part of what makes precious metals and gemstones so valuable is their ability to absorb magic and essentially become energy batteries for spellcasters. How effective the reservoir is depends on how experienced/talented the enchanter is, and how quality the material is. 

IE, a seasoned enchanter probably knows how to more efficiently activate a reservoir, and a diamond or piece of gold would have the potential to hold considerably more magic than a hunk of quartz or brass.  

As far as schools vs apprenticeship, it varies by location. Some major cities in Edessa may have schools, smaller towns and villages likely rely on apprenticeship. Edessa itself has no nation-wide magic school, short of its military academy, which teaches martial skills as well as magical skills. The Varyan Empire on the other hand, does have a national school of magic.