On the basics of Magic:
Magic, in essence, is the manipulation of the force that holds all life in the universe together. This force is often called Mana, but it has many different names as well. Chi, The Force, and other similar names. The beings in the universe all have varying levels of control over mana, if any at all. Also, magic treats each person somewhat differently. Some more than others. One magic user might be able to summon necromantic armies with their bare hands, while others might have trouble even conjuring a candle light. Regardless, the concept remains the same: mana is manipulated to achieve that which would be very difficult to do through normal means. In fact, some individuals might only be able to use a single type of magic impossible to be manipulated by any other being.
Wizards:
Wizards, in general, are beings who were born with the ability to simply control mana. Many go through their lives without knowing, or maybe in denial. As a wizard begins to develop his or her powers, they will notice that they can use mana to manipulate the four basic elements (Earth, Fire, Air, and Water) to a limited degree. Though some special cases find they can manipulate Lightning, Light, or Darkness in addition to the four basics. If a wizard wants to cast more powerful magic, one of two things must happen.
1. A wizard can create a tool in order to cast powerful magic.
2. A wizard must go through a profound moment in which a part of his soul is changed fundamentally, giving him the ability to cast certain kinds of magic without the use of tools. However, this is incredibly rare.
(Note: All this info is continually updated on a google doc linked in my signature)