Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
Wedding bells!
Othello and Desdemona fall in love and run away together to get married. Everything's peachy! Until Desdemona's father finds out…
Conflict
Interracial marriage not approved by Dad. Also, war and a villain.
The conflict comes in a few different forms. First, you've got Desdemona's dad all angry that his daughter secretly married a black man. Next, it looks like war with the Turks. Last and most importantly, you've got a livid Iago itching to wreak some havoc.
Complication
Iago hatches a plan.
While some of our conflicts go away (like the war and Brabantio, at least for the time being), others (Iago wanting to wreak havoc) lead to further complication. Iago is no longer an angry man; he's now an angry man with a plan. Not to mention, the convoluted machinations he devises are complicated enough in their own right, even without a classic plot analysis.
Climax
Iago convinces Othello that Desdemona's cheating and Othello resolves to kill her.
The intrigue of Othello is watching Iago work his manipulative magic. The deceptions grow, bit by bit, until Othello is quite ensnared by his own jealous thoughts. The plot thickens and thickens, and the complications twist and turn until we finally arrive at the psychological climax: Othello's declaration that he'll kill his wife. We chose this as the climax, rather than the actual killing, because we are building toward Iago's defeat of Othello's mind, not Othello's defeat of Desdemona's body.
Suspense
Othello will soon kill Desdemona.
Now that we know Othello's going to kill Desdemona, we get all worked up in the suspense of when it's actually going to happen. We're also not sure how things will work out for Iago. Will he get away with his plan?
Denouement
Almost everybody dies.
The denouement starts as soon as Desdemona dies. Minutes after she dies, Emilia figures out that Iago is responsible for the whole mess. When she shares this with Othello and his men, Iago kills her. Othello, broken by grief and guilt, stabs himself.
Conclusion
Bizarre silence from Iago.
Cassio survives. So does Iago, who refuses to explain why he did what he did and swears he will never speak again. It's an unsatisfying conclusion, since we wanted the cash-in moment where the detective explains whodunnit, and how he did it.