A more thorough explanation:

Legis actio sacramento was a legal action used in ancient Roman law. It was the earliest form of civil procedure. At the beginning of the legal action, each of the parties involved had to deposit or give security for a certain amount of money, called the sacramentum. The loser of the legal action had to forfeit this money to the public.

For example, if two people were in a legal dispute over a piece of land, they would both have to deposit a certain amount of money before the legal action began. The person who lost the legal action would have to forfeit their deposit to the public.

Another example would be if two people were in a legal dispute over a debt. They would both have to deposit a certain amount of money before the legal action began. The person who lost the legal action would have to forfeit their deposit to the public.

These examples illustrate how the sacramentum was used as a way to ensure that both parties took the legal action seriously. It also ensured that the loser of the legal action would face a penalty for wasting the court's time.