In the lower right hand corner of the screen, there is a symbol followed by a number. This number represents your Blood Count, often abbreviated BC. You can increase your Blood Count by killing mobs, but you may not receive a point for every mob you kill.
When your blood count reached 999, you will receive a message stating that a Blood Essence has been completed. The symbol will become a button, and when you click on it you will receive a Blood Essence.
When you die in a PvE scenario, your Blood Count will reset to 0. When you are killed in a PvP scenario, your Blood Count will not reset.
Contrary to popular belief, you do not gain a Good Karma point whenever your Blood Count reaches a multiple of 100.
Many players encounter a problem when they are in a PvP scenario, as they are concerned when they lose their BC. Your BC can be lost in a PvP scenario if you die as a result of a Bleed status effect.