Both Brutus and Antony speak to the crowd in this scene. However, their purpose and the outcome of their words is very different.
Brutus speaks to the crowd first. He wants to explain the reasons for killing Caesar. He tells the crowd that this was necessary in order to preserve Rome as they know it. He also tells us that Caesar had wanted to become a dictator, and that his death was for the best.
Antony, while supposed to support Brutus's decision, uses clever words and rhetoric in order to convey an idea of injustice. He reminds the people of how good Caesar was, inflaming their indignation and encouraging them to disagree with the conspirators.