I don't understand "The Tell-Tale Heart." Can anyone tell me about it?

"The Tell-Tale Heart" whose title means "tattle-tell," is a story of psychological horror.  The narrator, a madman, kills a man and boasts of his skill in doing so without detection.  However, in his madness, the narrator believes that he hears the heart of the dead man beneath the floor boards where the narrator has buried his victim.  Obsessed with this "sound," which is probably the nervous beating of his own heart, the madman tears at the floor boards and cries out, "Disemble no more!" giving himself away to the police who have entered his house in order to investigate a shriek heard outside.

Of course, all the horror emanates from the mind of the narrator who becomes fixated upon the eye of the old man whom he claims to love.  But the filmed eye, like that of a vulture, he blames for his killing of the old man.  Also, the old man intuitively senses that some horror awaits him as he sits up in bed, groaning, long before the narrator attempts any harm. This interweaving or "arabesque" as Poe termed it, of symbols that change in meaning (the lantern, the eye) has led the critic James Gargano to believe that the story is a doppelganger. A doppelganger is an apparitional twin or counterpart to another living person.  That is, Poe's narrator and the old man are both of the mind of the narrator, who projects his terror and shares his terror.  This is why the narrator "hears" the beating of the heart of the dismembered, buried old man.

See the links below which will help with this concept of doppelganger.