Kamma is an impersonal, natural law that operates in accordance with our actions. It is a law in itself and does not have any lawgiver. Kamma operates in its own field without the intervention of an external, independent, ruling agent.
Kamma or karma can be put in the simple language of the child: do good and good will come to you, now, and hereafter. Do bad and bad will come to you, now, and hereafter.
In the language of the harvest, kamma can be explained in this way: if you sow good seeds, you will reap a good harvest. If you sow bad seeds, you will reap a bad harvest.