which is easier to understand philosophy or ethics
Ethics is usually easier. There are less reading materials than in philosophy, and the units earned is also less. 6. Ethics is interesting but although philosophy is harder, your mind is challenged and you end up studying because you are interested vs you need to get through the subject.
Atheists unfamiliar with the basics of moral philosophy will be unprepared to discuss morality and ethics with theists. Atheists need to be able to respond, for example, to the claim that the existence of morality proves that a god exists, or that morality is impossible in the context of atheism.