Whatever the person does they get back equally. But it could happen instantly or it could wait until their end of life. Here’s some examples.
1: You backhand someone who didn’t deserve to be. Then immediately slip and hit you face as you leave.
2: You ruin someone’s life for your own gain. Live a great life. Then suddenly one day your wife and kids die in a house fire. You still have that money but your family is gone and it no longer matters. You may even kill yourself from depression or alcohol poisoning.
It’s just whatever has been caused by you, will come back to bite you.
Now karma caused by doing a cruel spell is worse. The rule of thumb for that is whatever you send out will come back to you times 3. So say you use magic to help a homeless man’s life turn around. You will have very very good karma some day. But say you instead send a curse to that homeless man and he gets hit by a car and dies. You will receive horrible karma.