Brutus convinced the plebians that Caesar was too ambitious and, therefore, needed to die. Anthony's speech, in an indirect way so the plebians don't realize it, opposes Brutus' argument and sets out to prove to the plebians how much Caesar loved Rome and its people and that he lacked ambition entirely. Antony uses Caesar's will to accomplish this.
Antony brings out Caesar's will during his speech in Act III, Scene II, but initially balks at reading it citing the rage it would bring them if they heard it. He gets them riled up to the point where they are begging him before he finally gives in and reads it. The will states that Caesar decided to divide his money and pass it down to all the people of Rome. It also mentions that he is going to give much of his land to the country, so the citizens could use it for recreational purposes. This gets the plebians to believe Caesar wasn't ambitious, but rather loved his country and its people immensely and, therefore, was killed at the hands of murderers.