Harm is divided into three levels of harm that characters can suffer. Characters can have multiple boxes in each level.
When you suffer harm of a specific level, but you have already marked all your boxes in that level of harm, mark a box in the next higher level instead. On the character sheet, simply move right until you find a free box.
When you suffer harm of a specific level, you ignore any boxes (marked or free) in lower levels of harm. In other words, when you suffer severe harm, you are immediately incapacitated, even if you have not suffered any harm previously.
Some characters are tougher than others, and one of the character Advancement options is to purchase additional harm bar splits.
This level of harm indicates bruises or superficial cuts and burns as well as minor toxins, poisons, diseases and such.
The main effect of these injuries is shock or temporary disorientation. You take a -1 die penalty only to the next action roll in the same scene. If you make no rolls for a good while or your character gets some rest after taking lesser harm, or the scene simply ends without you making another roll, you can avoid this penalty altogether.
This level of harm describes broken bones, deep cuts or injuries to vital organs as well as strong poisons, diseases, etc.
You take -1 die to all your rolls while suffering from moderate harm.
This level of harm represents life-threatening injuries, fatal poisoning and similar injuries that by themselves are extremely serious.
When severely wounded, you are incapacitated and can't act anymore beyond some moaning and a slow crawl unless you push yourself.