So, since good and evil are relative terms, I will start with MY understanding of the terms. To me, that which is "good" is that which flows, that which works, that which is in harmony. That which is "evil" is that which produces rotten fruit, disharmony, that which is the opposite of the "best path".
Now, in a very subjective sense, good and evil DO exist....because as a human, if I go and murder my next door neighbor, that is evil. Why is it evil? Because I have cut down someone's life in the physical form, robbing them of their freedom to live accordingly. I have unnaturally taken a life, before its time. I have plucked a fruit before it was ripe, so to speak. That would be considered relatively evil, to my subjective self.
However, in the GRAND SCHEME of things, evil is merely the other side of good. In a reality where anything is possible, you have spectrums. Light has a spectrum. Sound has a spectrum. Physical reality has a spectrum. Good and Evil can be seen as existing on a spectrum of free will, in a universe of conscious beings.
Since we have free will - we can either do an action that is harmful, or an action that is beneficial. In order for free will to exist, both options must be available. What I am trying to convey, is that evil is merely the opposite end of the spectrum of free will from good.
Ultimately, there is no good or evil. There is the One Source of all Things, and from that source emanates an infinite fractal matrix of oscillating dimensions of light and energy. When you look at a painting or a work of art, can you point out which parts of the artwork are evil, and which are good? No. You simply see the work of art as it is.