Dear Fatum,
The link you provided seemed to explain Karma from the perspective
of Hinduism. While the Buddha borrowed Hindu terms as pple then
were already familiar with those terms, the Buddha's teaching and
interpretation of these terms were often different. Karma and
Dharma as explained in the website are different from the Buddhist
Karma and Dharma.
Talking about Karma - the Buddha emphasized its difference from
fatalism. The Buddhist idea of Karma is beyond the extremes of
eternalism and nihilism. Karma, as the others explained, is not
about fixed destiny, it loosely means cause, condition and effect. It means
past causes, together with present conditions (which are also a
result of past causes), gather and come to fruition, which in turn
become causes and conditions in the future. Karma is a very complex
subject, which cannot be fully comprehended by a common
person.
Karma is very scientific. It is like... if you place an egg into
boiling water, and u pray very hard that it won't be cooked, after
10 min, u check, and it's cooked! that's it - the cause being u placing the egg into
boiling water; the conditions being there is sufficient
gas to ensure the water continues to boil, the pot bearing the
water isn't broken, there is sufficient oxygen in the air to ensure
u're alive to witness the cooked egg etc; thus the fruit of the egg being cooked.
U may have certain positive/negative seeds, but without the right
conditions, they can't come to fruition. The results may be
postive/negative, but depending on how we react to these results,
we create positive/negative karma. For eg, both of us may be having
headache, but I react to the headache by cursing/swearing at the
pple around me or feeling so much self-pity and getting depressed
over it; whereas you react to the headache by thinking that just
this headache already makes u suffer so much, not to mention the
kind of pain and suffering that other pple go thru when they suffer
from famines, chronic illnesses, starvation, wars, disasters, when
they get killed, etc... and then with that understanding u
empathize with these suffering pple and even generate the wish that
you could help to bear some of their suffering on their behalf.....
Well, same headache, but 2 different reactions, thus 2 different
karmic implications. 
Once there was a nun Ven Tenzin Palmo who talked about karma. I
can't remember all her exact words, but I tried to write down what
I recalled. I'll like to share her words with u, but really sorry
if I misinterpreted Ven Tenzin Palmo in any ways...
"What we experience now are due to the ripening of past karma.
There's nothing we can do about that. However, we have the choice
of how we want to react to our current circumstances, which in turn
plants the seeds for future ripening. You have the option of
reacting skilfully or unskilfully. When you understand this, you
are fearless, because no matter what happens, every situation that
you face presents to you as an opportunity to plant positive seeds
and engage in the spiritual practice."
- based on what I remembered from Ven's talk, may not be exactly
what she meant.
Another thing to emphasize, when Buddhism talks about karma, yes
it's about accumulating positive karma and eliminating negative
karma, but it's NOT just about that. When we do negative deeds, we
will not be punished by any being; likewise when we perform good
deeds, Buddha will not give us a gold medal.
Why karma is being taught - for us to understand that our actions
bear fruits and to be more mindful of it. However, the purpose of
engaging in Buddhist practice is for enlightenment, which is beyond
the notions and extremes of good, bad, not good not bad, both good
and bad. The aim of the Buddhist practice is NOT to become a moral
person, but rather to transcend beyond the societal concept of
morality and to accomplish the wisdom that liberates.
As Chandrakirti beautifully expressed,
"Those who are unwise will do a
lot of nonvirtuous things,
And as a consequence they will go to hell.
Those who are unwise will do a lot of virtuous things,
And then they will go to heaven.
Those who are wise go beyond virtuous and nonvirtuous,
And then they will attain liberation."
More reading if u're interested, from
http://deerparkgathering.org/introduction.html
Hope those ramblings help, and pls forgive me if they don't.
