Every mission in Dishonored can be played in one of two ways, either Low Chaos or High Chaos. A Low Chaos playthrough of a mission requires you to not get spotted at all by any guards or NPCs when sneaking around, as well as not killing anyone. A High Chaos playthrough of a mission doesn't require you to do anything, other than go completely wild, killing anyone and everything in your path.
Although the player can choose how to do each mission, for the purposes of the guide here, there will be two separate playthroughs of the game. One playthrough will be done in Low Chaos, while the other will be done in High Chaos.