OK lemme try and explain Aura; There are eight elements in FF2. Four are elemental (Fire, Ice, Lightning and Poison), whilst four are a bit odd (Dimensional, Mind, Body and Instant Death). Each enemy in the game has either a weakness or resistance to each of these, or perhaps they are indifferent. What Aura does is add an elemental unit to your physical attacks. If the enemy happens to be weak to that element then they will take extra damage. If not then nothing will happen to your damage output. The level of your Aura spell affects which types will be added. I don't know the exact order, but I do know once you reach Level 8 it will add all types of elemental attack. By the by, Barrier follows the same principal except it increases your defense, and Dispel again except it lowers the defense of the enemy to an element. I'm not sure what Wall does however...
