The Karma acts like your bank-balance. The more positivity than the negativity you have in your bank (karma Bank), the karma gives you almost what you wish for. When the negativity rises more than the positivity, the karma brings you bad luck (punishments).
Sometimes Karma doesn't wait for the negativity to grow above positivity, it attacks you with some disaster (small or large, to you or to your near ones or to your belongings) when there is the need to do that. Sometimes the Karma also doesn't wait for the positivity to rise well above the negativity, it gives you some gains and gifts. So create a shield of +ve energy around you that will stop you from doing something "that's not good", and attracting "curses"/ill-feelings/accidents/misfortunes/... IMO, Karma is the result of any action that we are doing all the time. What we do can be +ve, -ve, neutral... It will keep building that bank balance...
IMO, one can also lend/gift a part of his/her karma to someone else -- good, quite easily, and bad, only if you know how to "give" it to some one else.
Some people with advance knowledge can easily pass on another person's Karma to someone else individually or to a crowd, and vice versa. It's funda is a bit difficult to grasp initially...