Can anyone help me with fuel system treatments?

I was having some trouble with my car recently, and someone told me that i had “bad gas”. I’m assuming that gasoline is like water or juice for cars, and anytime i get something that tastes bad, I add sugar. My friend assured me that it was a good idea, so should i add a cup of sugar straight to the tank….? or do i need to mix it thouroughly in a can first?