In order to cast spells, a magi must first find a master to teach him the basic rudiments of the craft, just like any other craft. The master must be of the same sphere as the student.
The spells, however, must be discovered by the student himself in his studies. Magic, even if of the same sphere, is manipulated in different ways by different spell-casters. Therefore some can cast spells which others can't, some pick up concepts quicker than others and some never progress past the first stage.
Spellcasting is the manifesting of strange powers unknown to sages and scholars around Telandron; still unknown to this day, despite a vast amount of research into the subject. The term "sphere" is a massive simplification. Spellcasting enables magi to perform tasks which they would normally not be able to do. Like these tasks in normal life, there are varying degrees in strength between magi.
Much more will come to your character when he becomes apprenticed to a mage. Instructions will be given from the master to his pupil.
Another aspect of spellcasting is the chant. Basically a spellcaster uses the chant as a key to unlock the gates to this mysterious power he holds within him. A different chant is used for each different spell that needs to be cast. Again, when researching and studying his own powers the student will discover what chant is needed to unlock this gate.
For most spells some magical ingredients are needed. They for the most part are mundane items that can be easily bought or in some cases found. Such items include a single gold piece, a dagger, some silk, rope or any such item. However, as the spells your character attempts get harder, the objects needed for the spells become more challenging to find and obtain, for instance quicksilver, gold-dust and unicorn horn. These can also be very expensive.
Lastly, spells can be either made temporary, in which case your character will be told when the timer runs out on your spell. Or, at the cost of vast materials, time and gold, a spell could be made permanent. Only, however, should this be attempted in total peace, for several hours of concentration is needed for the most simple spells to be permanent.