Magic is the combination of mana and the world elements, directed by the mind through visualization, one can manifest all kinds of different phenomena.

So what are magic circle, sings and chants?

Well they're nothing more than a simple form of self-hypnosis. How?

As visialization is needed in order to use magic, a great deal of focus is put into it. You can't stand still as the enemy is shoting his arrows at your direction, can you?. No you need to keep moving, so in order to properly use magic chants and hand sings were designed, the same with runes and magic circles, they are psycological tools used to help the maind of a mage reduce the amount of focus used while casting a spell. That's also the reason why shouting a spell's name produce better results than simply casting it in silence.