Karma originally means "work" - intended actions.
Let's imagine we travel outdoors and find a good fruit. We eat it, it's tasty, then we go on. With regard to that experience, we can do different things, for example:
- We can develop clinging and desire to find more such fruits. So we put a lot of our energy in searching.
- We can let it go and just travel further, not bothering about more fruits. Realizing that we can find them, we remain attentive, but we do not invest our energy in searching. We continue to enjoy the travel as a whole, not losing the sight of the sky and everything else.
Then if we find more fruits, the result would depend on the attitude we developed:
If we have developed desire and clinging, we might feel fear that someone else might come here too, and take a part of "our" fruits. We develop greed and eventually regret that we don't see even more fruits.
Since that, finding fruits, we will feel vexation: excitement with a bit of fear, greed, jealousy and regret.
And when not finding enough fruits, we feel regret and anger (and greed, and jealousy to those who also found some).
But if we didn't develop desire and clinging, we didn't invest our emotional energy into the search, then we will remain calm and easy. New fruits wouldn't lead to vexations, and when we meet others, instead of jealousy and fear, instead of wishing to hide our fruits from them, we would like to share, to give them the fruits we found.
That's how karma works.
- Ignorance (Avidyā) - encloses our limited perception. It creates limited models -
- Mental creations (Saṃskāras) - such as "it's good to find such fruits", leading to -
- Consciousness (Vijñāna) - limited view of the world, such as becoming busy with chasing fruits, and neglecting other things in our travel -
and so on (see Twelve Nidānas).
Briefly speaking, intentional work, accompanied with limited consciousness, develops desire, and then both good and bad events would cause vexations.
That is the power of karma: we put our energy in something limited, it's like putting there a part of ourselves. Then that energy works separated from us. Thus we have lost our wholeness.
We feel that "external forces" influence us, pushing us to feel vexations, and pushing us to do this or that.
This is called karmic impulses.
In fact what really hooks us is not external forces, but our own energy which we invested earlier, separated from our wholeness.
Imagine this as particles of various colors, which we have thrown in some mental space. They got kinetic energy, so they remain flying in the space. That is called karmic seeds.
When we meet again with such particles, that kinetic energy pushes us to act and to perceive the world according to their direction, speed, color, etc. It is called manifestation of our karma.
So in order to remove our karma we have to withdraw our energy from the desires we developed.
It's just like habits: bad karma is bad habits, good karma is good habits - such as sharing with others, being friendly, kind and attentive, etc.
The point is to change our habits, just in Buddhism we analyze them really deeply, so we are able to find their weak spots and change them very efficiently.
PS. With this explanation you can understand why with bad karma we meet enemies where with good karma we meet friends.