Karma can have different meanings for different people.  Essentially it is a momentum of energy that is based on vibrations from previously.  There is only ever the now to work with, and so prior momentum – wherever it may be from – can only be ‘active’ in the now. 

You can set your course in your now moment, whether it be from prior momentum (wanted or unwanted) or by deliberate intent of what you would like, and that is through your focus of attention on what you would like more of.  As you do that you are creating momentum for that, and you are setting your course