The first thing that comes to my mind at the mention of the word 'evil' is that there is no such thing.
If a baby and a puppy and some kittens are burned to death in a house fire set by an arsonist, we see the arsonist as evil. But in reality, he is a psychopath and something is messed up in his brain. The fire is not evil. Certainly the deaths of the living creatures are not evil in itself because every living thing must eventually die.
The word 'evil' is used to describe something that offends us. But there are many things that can offend a person that are not considered evil. A rotten smell can be described as 'evil', but another person smelling the same thing may not be offended at all, so it is not inherently 'evil'.
The opposite is true for the word 'good'. If something pleases us, it is a 'good' thing, right? But to the arsonist above, he saw his act as a pleasurable thing.
So, to sum up. good and evil are relative. The words are assigned as labels to what makes us feel good or bad. God is 'good' and Satan is 'evil', but not to everyone, so these are just labels applied according to how a person feels.
Feelings are whimsical. They mean different things to different people. What is evil to one person is not necessarily evil to another person. Evil is a label, not an actual THING.
To test this, try to draw a picture of 'evil'. You can only draw what YOU think of as evil. There is no one THING that a picture can be made from. Nothing that everyone in the world will consistently draw a picture of.
Good and evil are judgement calls.