In "The Tell-Tale Heart", what is the climax?

Your original question asked more than one question, so I
have had to edit it down to focus on the climax of this terrifying story. Let us
remember that the climax of the story comes after the rising action, where the story
reaches its high point, or the stage at which the reader is most engaged and excited
about what is happening. It comes before the resolution, when the conflict is resolved
and we are given our ending.

It is clear then that in this
story, the climax actually comes when the policemen come to visit, alerted by a
neighbour about the shriek that was heard as the narrator killed the old man.
Interestingly, at first, the narrator is completely nonchalant about their
arrival:

I
smiled - for what had I to fear? I bade the gentlemen welcome. The shriek, I said, was
my own in a dream. The old man, I mentioned, was absent in the country. I took my
visitors all over the house. I bade them search - search
well.

The narrator clearly
feels that he has nothing to be worried about, having concealed the body. He talks of
the "wild audacity of my perfect triumph" as he revels in the fact that the policemen
sit in the same room where he has concealed the corpse. The policemen are obviously
satisfied, but stay talking to the narrator, until he begins to hear a sound, which with
terror he realises is the sound of the old man's heart, still
beating.

It is this point that is the climax, as the sound
of the heart becomes ever louder, driving the narrator insane and causing him to confess
to the murder that he would have otherwise gotten away with.