In this scene, we get a good glimpse of Othello's jealousy and anger. Othello's jealousy and anger was initiated when Iago had planted the idea of Desdemona having an affair into his mind. Othello punches Desdemona. Two big factors and themes we can recognize from this scene, is Othello's anger/jealousy and the power of Iago's manipulation.
In this scene, Othello tells Iago to confront Cassio about Desdemona and that he'll be overhearing the exchange. Iago strategically leans in close to Cassio (so that Othello cannot hear the sentence) and basically switches the person they're talking about from Desdemona to Bianca. Cassio goes on about how beautiful she (as in Bianca) is, however it seems as if he's talking about how beautiful Desdemona is. More proof is offered when Cassio admits to Iago that he gave a handkerchief to Bianca (which was Othello's). Through Iago's manipulation and power, he turns this scene into a very important one.
In this scene, Roderigo is sent by Iago to kill Cassio, but does not get the job done. Both Cassio and Roderigo wound each other, and Cassio makes a run for it asking for help saying that someone has stabbed him. Iago comes running into the room to see a wounded Roderigo. Iago's deviousness leads him to finishing off Roderigo by stabbing and killing him, then realizing that he did not need Roderigo anymore.
In this scene, Othello confronts Desdemona who admits to him that she does NOT have the handkerchief which represents Othello's love. The handkerchief was the last straw and ultimate proof for Othello that Desdemona had an "affair". After much exchange and fighting, Othello strangles Desdemona and suffocates her to death.
In this scene, Emilia comes to the realization of what Iago has done by manipulating everyone and causing such crazy turn of events. She starts yelling at him and Iago ends up stabbing her, as she would slowly die in this scene.
In the end, because of Iago's manipulation and overall power/influence throughout the story, and Othello coming to the realization of his jealousy/anger and how he just killed the love of his life for no reason, he commits suicide by stabbing himself.