Definition:
The phrase "in force" means that something, usually a law, rule, or agreement, is currently active and must be followed. When something is "in force," it is effective and has power or influence.
In effect: This is a similar phrase that means the same thing as "in force." You can use them interchangeably.
Force (noun): The power or strength that can cause changes or movement.
Put into force: This means to start or implement a law or rule.
Come into force: This means that a law or rule starts being effective.