To cast a spell, first drag its icon onto the hotbar located by default on the top left of your screen. You also need to have a staff equipped. Press R to ready your staff. If your desired spell is in slot position 1 you press the 1-key on your keyboard to ready your spell. You can see your spell is selected as the active spell at the bottom of the hotbar. Now you're ready to cast the spell. Press and hold the left mouse button to cast. When you have your target in sight, release the mouse button to fire your spell.

If you're wearing a lot of armor, or very heavy armor, you'll have a penalty to your damage output with magic. Your chance of misfiring your spell is also increased. However this can be offset by raising your Armored Magic skill which goes up while casting spells in armor.

As you raise your skill in Lesser magic, new spells and new schools start becoming available to you. Visit the Mage NPC to buy new spells and new schools of magic.

More advanced spells require reagents to cast. In order to become good at magic, you need a lot of time and a lot of reagents. However the rewards are worth it as a powerful mage can influence a battle in an impressive way, healing and buffing allies, damaging and debuffing enemies etc.