Explanation:
First, a quick recap:
Nonessential elements of a sentence are words, set of words (phrases) or clauses that can be left out of the sentence without altering its meaning, unlike the essential elements which have opposite feature.
Introductory phrase is a set of words that provides setting for a sentence.
So, for example, we could say:
A: William Shakespeare, famous writter, wrote many plays.
B: The dog that I found by the river hates swimming.
C: On monday morning, luckily, I found my keys.
D: I visited Paris, the capital of France.
Note that nonessential elements are always separated by commas.
"The Pit and the Pendulum" tells the story of a man who was tried and condemned by the sponge inquisition and although he is not fully convinced of what is reality and illusion, he feels that he has been condemned to death. He feels stunned by it and strongly confused and fearful for the sentence he received and for the unpredictability of what will happen ahead.
The convict describes his prison with a strong synesthesia, he reveals all the psychological and physical terror that has passed, which disturbed him deeply amid hallucinations, sounds, images that appeared around him, bruises and a strong mental confusion. The prison is a claustrophobic, dark and frightening space, built with the aim of torturing and going crazy.
During the torture section, the convict is tied under a pendulum that contains a very sharp blade. The pendulum swings from side to side very slowly and is above the prisoner's body, but he realizes that as time passes, the pendulum descends more and more, even cutting his chest slowly and agonizingly. However, the prisoner manages to free himself from the ropes, but realizes that the walls are heating up quickly leaving his breathing, already weak, increasingly weak. In addition, the walls are coming together making the prisoner have no choice but to jump into the well built right in the middle of his prison.
The well and pendulum shown in the story are strong references to the methods of torture used by Spanish inquisitors who wanted to kill their victims in a slow and agonizing manner.
The first means of achieving coherence which the speaker mentions is the logical bridge.
I can't write the whole summary for you, but writing a summary is quite easy. Just take the main point of each chapter (in your case). Write the main point and what it caused. Kinda like cause and effect. Do this for each chapter. :) If you need anymore help, please feel free to ask! Hope this helps and have a Happy New Year!