Well, I think the task is pretty clear, isn't it? You have to check whether the given formulas are equivalent or not. That can be done in many ways as discussed in the lecture, either by making truth tables for both formulas, using sequent calculus, transforming one formula to the other by means of Boolean algebra or converting both formulas to a canonical normal form to compare. Anyone of these methods can prove the equivalence or disprove it. In case the formulas are not equivalent, there is a counterexample, i.e., a model that satisfies one of the formulas, but not the other one. That model can be written down as an assignment to variables or as a cube as mentioned in the exercise text.