MnO2 (s) + 2 FeSO4 (aq) + 2 H2SO4 (aq) → MnSO4 (aq) + Fe2(SO4)3 (s) + 2 H2O (l)
This is an oxidation-reduction (redox) reaction:
MnIV + 2 e- → MnII (reduction)
2 FeII - 2 e- → 2 FeIII (oxidation)
MnO2 is an oxidizing agent, FeSO4 is a reducing agent.