I'll give it a shot, a few minutes upon waking, and with only a few sips of coffee
I'm not Hindu, nor do I believe in god. I don't believe in heaven or hell. I do believe in karma, reincarnation and the like.
To me, karma is the running tally of this life and the past lives, the sum of actions and decisions made, which in turn brings on new situations and choices to make. There is no black and white, absolute right or absolute wrong.
A simplistic way of thinking about it, from a book I once read, compared it to black and white marbles. Through the time from birth to death, each action and reaction receives one or more marbles - some small actions are worth one - a tiny kind act, a petty lie, some receive many - saving a life, killing without cause. Some are mixed - not paying attention and crashing into someone's car, but then helping the victim etc. At the end of one life and the beginning of the next, all of the marbles are sorted and counted. Perhaps a change from white to black, an increase or decrease determines where the next life starts, and what tests are to come. I don't know, and that is OK.
I don't think I'm making sense....oh well. Yes, I believe in it. I also believe that while it's good to do right, it's not good to do right for the wrong reasons - trying to karma bank on greed, or because you want to go to "heaven", or to show how good of a person you are.
There is no end goal, just a changing line of rise and falls, and changing tasks and situations to navigate.
As for karmatic paybacks, I don't really believe that doing good automatically means good comes to you - it merely allows you to have alternative choices available to continue to do better or worse. If you are born into poverty, you still have choices - you can steal, rob and cheat, and end up in jail with minimal options, or you can sit tight, study, do kindness when possible, and get a scholarship to college and have many options. Sometimes karmatic good doesn't come around until the next life, and you are born into more options and better living, which carries it's own decisions to make.
Maybe I'll try this later.....once I'm caffeinated.