That is then handed to the police, and on authority of the court, police show up and use force/guns/handcuffs to take you to jail.
When the judge/jury says "Guilty", by the authority of the court you are then taken, using the same means as before to prison/jail and forcefully held.
All of these actions stem from the authority/direction of the court. It is the court's responsibility to enforce. They have agents acting on their behalf to actually do the work, but it is the courts which enforce.
The Philosophy Of Liberty -