Chaos is the system Dishonored uses to determine the decisions the characters make for you in the game. Kill more people you have a high chaos level resulting in more negative effects & vice versa. I've only realised this after completing the High Overseer mission. I don't really want to start the game again so will continue playing the remaining missions trying to get a low chaos level to balance out the earlier missions.

If I had the time I would carry on playing the way I am & then play the game again assuming it has a new game plus option to go for the low chaos ending.

During my new game post I wrote "I keep wishing for a Splinter Cell style radar to show me where enemies are". Runes are what give you supernatural abilities, after a visit by the outsider & session on how to use Blink (teleport distances) I used my first collected rune to unlock 'Dark Vision' which lets me see any person or animal & their sight zone.

I have now collected quite a few runes & have unlocked Dark Vision stage 2, Vitality, Agility & Shadow Kill which turns unaware foes to ash (this is useful because it means I do not need to hide bodies).

Another collectible in the game are Bone Charms these grant you an effect when activated. I have quite a few of these like River Affinity which increases my swimming speed.

I have not played the Thief games by (Looking Glass/Eidos) but I imagine that Dishonored borrows quite a bit from that series? I have not said much about the storyline, you are Corvo a bodyguard to the Empress & after she is attacked & killed you are sent to prison. You then obviously escape the prison & set out to avenge the death of the Empress whilst also finding her daughter.