You can find that Here.
The idea behind Karma is a simple one:
Do good onto others, and good things will happen to you. Do bad onto others, and bad things will happen to you.
Now, karma may not be that black and white, and many people don't believe in its existence at all. They may say something like:
"There is nothing to suggest that some omni-potent force keeps track of the things you do."
And to them I'd say yeah, you're right. There is nothing to suggest that.
But I'd argue that they should look at it differently. I don't think thats what makes karma plausible.
What makes karma possible, is the intention behind it.
Attempting to come from a completely non pseudo-scientific stand point, thoughts, and, by extension, intent, absolutely hold sway over our experiences (in other words, our reality).
For example, how do you choose to do anything? You must first think about wanting to do it, and then you take the proper steps necessary to bring yourself into experiencing that which you want to do.
Think of it like this:
When you do good things, you are coming from a positive mental state. Your thoughts are in line with the good you are doing, which, in turn, makes you feel good. If it didn't, you wouldn't do it in the first place.
This, consequently, sets you up for having a higher likelihood of experiencing good things, because thats the space your thoughts are coming from.
The inverse, doing bad, would also be true.
Basically -
when you do good (or bad), you bring yourself into a positive (or negative) mental state, making the odds of your subconscious leading you towards other positive (or negative) experiences more likely.
Or something like that.
There is a reason highly successful people use methods such as "acting as if". If you tell yourself you are that, or will experience that, you will only increase your likelihood of doing so, as your thoughts, and, as a result, your actions, will become more in line with your intention.
I hope that makes sense.