The topic of the belief that a Muslim should have in the last day could literally fill volumes on top of volumes. There are so many different facets of what we believe in and about, in reference to that day. So I will try to be brief, and talk in general about about that which the day of judgement consists, about which we must believe.
From the affairs that we need to both know and believe in is the resurrection after death. We must also have a firm belief in the being in front of Allah, the reward, the punishment, the scale, the bridge, the paradise, the Fire. These are only some of the things in which we have been commanded to believe in as Muslims. For those looking for more information about this topic, you can reference our E-Book on the topic in sha Allah.