well you can defend yourself with magick. you can't freeze a bullet, or stop time to avoid an attack, but you can make charms or cast spells to protect yourself, the people around you, and your possessions from harm.
magick is used to create change in ones life. most will got he positive root [such as luck or healing] but you can use it for revenge on people you feel deserve it. it's all morality really. as for magick's uses, it's using natural energy to create change in your life, good or bad. it cannot go against nature, but it can make your life easier.