After accepting the mission from Ken, you'll be given the locations of two jurors on your mini-map. They are marked as pink icons. The first juror is usually found near the courthouse. Get into a fast car and head towards the first marker. You'll need to act quickly, as the jurors are on their way to the courthouse.
Upon reaching the first juror, they will attempt to flee in their car. Your objective is to stop them. You can do this by ramming their vehicle repeatedly until it's too damaged to drive, or by blocking their path. Be careful not to destroy their car completely, as you need them to be alive for the intimidation.