The narrator is confessing what he did to the old man and why he did it.
"I stared into his room for 7 nights in a row". The Narrator is saying that he stared at the old man in his room for 7 nights, and he was planning to kill the old man.
"In an instant I dragged him to the floor, and pulled the heavy bed over him". On the 8th night the narrator has made a plan already, then he finally decided to kill him after the evil eye looked at him.
"I dismembered the corpse. I cut off the head and the arms and the legs." The narrator cut off the old mans limbs and hid them under the floor boards of the house.
"There was a knocking at the street door. I went down to open it with a light heart,--for what I had to fear? There entered three men, who introduced themselves as a police officers of the police". The narrator went to go open the door to the police officers.
"The beat grew louder and louder until i can't take it anymore". The narrator is confessing what he did to the old man, and how he heard the heart beat during the officers at the house.