God had told Adam not to do something and Adam chose to do it. This hurt their relationship. It broke the relationship that God had intended for Adam. The penalty was separation from God. When this happened to Adam, it introduced sin into the human race. The Devil is real, and his job is to keep us in spiritual death (John 10:10) Scripture explains that everyone has sinned and therefore we are all guilty like Adam (see Romans 3:23). Because of that the penalty is separation from God, which is spiritual death (Romans 6:23).
But God loves us and provided a solution to the problem.