Policies are not written to stay on a shelf. Every line in every policy should be tied to a risk that the organisation needs to control. As such, each policy needs to be communicated to the people who need to follow the policy.
What should be communicated? Whatever is relevant to that employee.
When should it be communicated? Before the employee starts to access and process the systems and information that they are expected to handle in accordance with policy.
Else what's the point? "We've written this handy guide on the important things you should know about flying a plane. Don't worry about reading it until you have flown passengers around a bit."
The question assumes that there is a set (a set of 4, in this case) of core things in the policy that is a higher priority than the rest. What those things are will be potentially different for each organisation because the risks that an organisation needs to control are different for each organisation.
In short, the question is hyper-specific and wants the answerer to understand what the most important things are in the policy. We cannot know that without understanding the policy.