What exactly is 'Spell' and how and what makes them effective?,like in doing a ritual is it about the law of?

attraction,what you put out you get back?there are so many religions that practice spell-work do they all have somethng in common like witchcraft,voodoo,is it just a way of life doing spell work ,since there is so many different ones like some ask the god/goddess for help to make there spells work some ask spirit,do you always have to call on someone ,what actually makes a spell come true?