In Heimr, good and evil are words that describe the morality of actions. What is good and what is evil are not things though up by mortal philosophers. What is good and what is evil is strictly defined by Ratish, the god of morality, this is stated in Genesis 1 verse 1 sentence 5.
Ratish defined "evil" acts in the following way: "If you think somebody else will be harmed by your act and you think the other will be angry with you if he knew about the act the act is evil."
This is the definition of evil as defined by Ratish god of morality.
This definition is not open for interpretation. It has been defined by Ratish and therefor it simply is.
The trick of this definition is in the world "think". If you think something on Heimr you are fairly certain that something is. You probably realize you might be wrong but you are so certain of it you base the action around the assumption.
So, in other words, if you are fairly certain that you action harms somebody else and you are fairly certain he would get mad, but still do it anyway, you are committing an evil act.
If you steal something, you are harming somebody else and (if you are stealing from a sane human being) he is going to get mad if he ever finds out.
Doing this however is not an evil act if you are not aware that you are harming somebody. You have to think you are harming somebody. So somebody who lives in an society that has no form of "possession" and comes in a society that does, doesn't know he is harming somebody if he steals, therefor he is not committing an evil act (he will probably still be punished for it though).
Doing this is also not an evil act if you are not aware of the fact that the other will get mad. If you steal something from somebody, but that somebody is a good friend and you need the item now badly and you friend isn't around to ask, the friend will probably not be angry if he knows the truth about the situation. You know this (or at least, you think you know) so you are not committing an evil act.
Execution of criminals is an evil act however it is probably also a good act. You are doing it to enrich the lives of other who you probably never met and never will meet. Acts can be good and evil at the same time.