This is based on the material that my professor have given me. I have simplified it slightly and wrote some important points down.

The Dark Arts: An Introduction

• it is a term that covers anything that has the intent to harm, injure, or even kill another person


• includes different branches of magic, particularly potions and charms


• used actively and mostly by those who has the desire and actively seek power


• there will be no turning back once you have cast a dark spell, it will continue to corrupt you, making you impossible to resist the power you felt when you used it


• it corrupts ones soul and body


• the scariest part of the dark arts is that it can never be defeated or conquered, it is only possible to be held back for a certain period


• there a five main categories of the dark arts : dark potions, dark spells, dark creatures, dark artifacts and dark practices

The Dark Arts: The Three Spell Categories

Jinx:

• first and lowest level of dark spells


• usually does not cause much harm and will only cause minor irritation


• irritating and can be used as a form of distraction, but will not cause any lasting damage

Hex: 

• second classification of dark spells


• abit darker than the jinx and would cause more lasting damage


• causes major inconveniences and moderate amounts of sufering


• can be reversed with a hex breaker

Curse:

• darkest and most dangerous classification of the dark spells


• severely harm or potentially kill the target


• use of these spells are discouraged unless absolutely necessary


• there are also three unforgivable curses that could earn someone a lifetime stay in Azkaban 

That's all for defence against the dark arts.

i hope that it was helpful!