"We are the heirs of our own actions." ~ The Buddha
In Sanskrit, karma means action. We create karma through thoughts, words, actions that we execute ourselves, as well as actions others do via our instruction. Moreover, it is through our karma that we perpetuate samsara, the cycle of cause and effect; past and future; and birth, death and rebirth.
In essence, the laws of karma are not meant to punish. Rather, they are simply the manner in which all things are set right and returned to balance. Most frequently, we generate negative karma though our desires and longings. We also create negative karma because of ignorance. Often, we simply do not know any better. Even with our best intentions, negative karma can be set into motion when others are harmed by our actions.
As long as we see ourselves as the victim of old, accumulated karma, samsara continues. On the other hand, through right and thoughtful action, we can mitigate the effects of past karma. First and foremost, we must be willing to take responsibility for our habitual swinging between pleasure and suffering. From this vantage point, we begin to see that we construct heaven and hell in our own lives. Moreover, we understand that we are the ones with the capacity to respond to any life situation through either acceptance or resistance. With this realization, the wheel of karma begins to wind down its relentless motion and eventually becomes still.
Finally, Nirvana is the complete and total liberation from karma. In the absolute sense, we are not separate from our actions. When the doer recognizes that he is inseparable from his actions, he also becomes aware that the actor and action arise and subside simultaneously. Therefore, in a state of total self-awareness, right action takes place quite naturally much like a stream, flowing easily downstream. As Tagore reminds us so perfectly, "Nirvana is not the blowing out of the candle. It is the extinguishing of the flame because day is come."