Once you've stopped the first juror's car, they will exit and attempt to run away on foot. Chase them down and beat them with your fists or a melee weapon (like the baseball bat you start with). You don't need to kill them, just inflict enough damage to make them scared. A few hits should suffice. Once they've been 'persuaded', they'll run off.
Repeat this process for the second juror, who will also be marked on your mini-map. The second juror might be in a different part of the city, so be prepared for another chase. After both jurors have been intimidated, the mission will be complete, and you'll receive a cash reward. This mission teaches you the effectiveness of direct action in Vice City.