The difference between good and evil can probably be best shown with light and dark. Darkness is the absence of light. By removing the light, you have darkness. You do not add anything, just remove. But can you remove darkness? Taking it away does nothing. The only way to get rid of darkness is to introduce light.
The same could be said of good and evil. But can’t I get rid of evil just by doing less of or removing it? Well, that depends on what takes the place of the evil. If you replace it with good, indeed you are getting rid of the evil. But you cannot replace it with nothing. Something must take the place of what you removed.
If you stop doing evil, you are doing good. If you do less evil, you are still doing evil. But can you do less evil? In a sense, you can. Every time you do less evil, you are doing more good. The goal though is to always be doing good. Indeed, that is what we will do in Heaven. We need to practice before then.
Evil is the absence of good, much like darkness is the absence of light. Many times, we do things that have some evil and some good. Telling the truth is good, but not doing it lovingly is evil. There are many things that we do. Our intentions affect our actions. If I was to share the truth lovingly, I would share it in a completely different way than when I want to win an argument.
So, if you want to be good, do not just try to remove the evil, but fill it with good. Otherwise, you will find that you did not remove anything. An old Chinese Proverb says it pretty well, “better to light a candle than to curse the darkness.” It is up to us to be the brightest lights that we can be.