How initiate the dark brotherhood sacrament? it's simple. First, you must go to Windhelm. Went over there, you must go to a little boy named Aventus Aretino, which is in the process of convening the black brotherhood. There you have to talk to him and he will ask you to kill an old lady who takes care of the orphanage because her mother died of an illness during the winter. He seeks the revenge we now cover about the owner of the orphanage. It will kill Grelod Riften who lives in a small house, you will find children with an old lady, it's the old lady that you must kill. Then you need to sleep in a hostel for 24 hours. When you wake up you will find yourself in a cabin forsaken with Astrid, the leader of the black fraternity and three prisoners, you have a choice: you can kill Astrid and then destroy all the black brotherhood, OR you kill one of the prisoners you and Astrid initiates into the black brotherhood. We must do all the quests Astrid request. You will have a nice equipment to kill each of your victim.