Spells are very helpful. When you cast a spell it usually consumes an amount of mana. If you don't have enough mana then you cannot cast the spell.

You will be able to get many spells during the course of the game. You get spells by purchasing and using spell scrolls. Many NPCs in the game will also teach you spells for free or for a price.

Clicking on a spell name will show a description of each spell and the mana it requires