The setting of the story is Toledo, Spain, during the Spanish Inquisition. The narrator has been arrested, tried, condemned, and imprisoned in a cruel and inhumane way.
The conflict, I think, is that of character vs. self. The narrator loses consciousness as a result of his fear several times, and he struggles to control that fear and to remain calm so that he can retain consciousness as well as sanity. He talks about the "agony" of his imprisonment and each of the new terrors prepared for him. He might have opted to jump into the pit, or he could have lapses into unconsciousness due to fear while under the pendulum, but he fights feelings of hopelessness and keeps his head, and this is what enables him to survive.
There is mainly only one character: the unnamed narrator. His judges come and go fairly quickly at the beginning of the story, and General Lasalle, his savior, appears for just a moment to save him at the very end.
The point of view is first-person objective: this means that the narrator is a participant in the events of the story (and uses the first person pronoun "I") and that he narrates the events after they occur (instead of while they occur). You can see that he uses past-tense verbs, which indicate this timing.