If an object is at rest, it will stay at rest until acted on by some external force. A pen sitting on the ground will continue to sit there until some external force moves it from that position. That external force could be from my hand picking it up or someone's foot accidentally kicking it.
If an object is already in motion, it stays in motion unless an external force stops it. If no external forces are acting on that object, it will continue at the same velocity forever. If there was a never-ending patch of ice that was perfectly frictionless, a person could slide on that ice forever unless an external force stopped them or changed their velocity.
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