Karma is the concept of “action” or “deed”, understood as that which causes the entire cycle of cause and effect.

Some traditions i.e., the Vedanta, believe that a supreme being plays some kind of role, for example, as the dispenser of the ‘fruits’ of karma or as exercising the option to change one’s karma in rare instances. In general, it is consider the natural laws of causation sufficient to explain the effects of karma. The individual is considered to be the sole doer and enjoyer of his karmas and their ‘fruits’. Laws of karma are codified in some books.
Some people disagree that karma is merely a law of cause and effect but rather is also dependent on the will of a personal supreme God. A summary of this theistic view of karma is expressed by the following: “God does not make one suffer for no reason nor does He make one happy for no reason. God is very fair and gives you exactly what you deserve.”

Karma

Karma is not punishment or retribution but simply an extended expression or consequence of natural acts. Karma means “deed” or “act” and more broadly names the universal principle of cause and effect, action and reaction, that governs all life. The effects experienced are also able to be mitigated by actions and are not necessarily fated. That is to say, a particular action now is not binding to some particular, pre-determined future experience or reaction; it is not a simple, one-to-one correspondence of reward or punishment.
Many Western cultures have notions similar to karma, as demonstrated in the phrase what goes around comes around.
The idea of karma was popularized in the Western world through the work of the Theosophical Society. In this conception, karma was a precursor to the Neopagan law of return or Threefold Law, the idea that the beneficial or harmful effects one has on the world will return to oneself. Colloquially this may be summed up as ‘what goes around comes around.’

Theosophy also teaches that when humans reincarnate they come back as humans only, not as animals or other organisms.

Karma does not necessarily mean past actions. It embraces both past and present deeds. It is this doctrine of Karma that the mother teaches her child when she says “Be good and you will be happy and we will love you; but if you are bad, you will be unhappy and we will not love you.” In short, Karma is the law of cause and effect in the ethical realm.
Karma could be both the activities of the body or the mind, irrespective of the consideration whether the performance brings fruition immediately or at a later stage. However, the involuntary or the reflex actions of the body cannot be called karma.Every person is responsible for his or her acts and thoughts, so each person’s karma is entirely his or her own. An individual is responsible to shape his own future by schooling his present.

According to the ways of life chosen by a person, his karma can be classified into three kinds.  Satvik karma, which is without attachment, selfless and for the benefit of others.
Rajasik karma, which is selfish where the focus is on gains for oneself.
Tamasik karma, which is undertaken without heed to consequences, and is supremely selfish and savage.