What do communists believe?
Depends on how orthodox they are. The thinking of orthodox Communists begins with the ideas of a philosopher named Hegel who saw social history as a series of conflicts between what he called Thesis (the established order of a given time; land-owners during the Medieval, Capitalists now)and Antithesis (the new, more advanced political power of a time: capitalists during the medieval…). Thesis and Antithesis would, per Hegel, fight it out for a while before unifying into Synthesis, a new order that would become the Thesis of the next conflict. According to Marx and, again, the orthodox commies, communism was the final perfected society resulting from this history of conflict, the ultimate and lasting Synthesis. Less orthodox types, however, usually see it as simply a way out of what they perceive as oppression by the rich.
The simplest version is “From each according to their abilities, to each according to their needs.” Communists believe that the only way to become rich is to exploit other people. They believe that all property should be held in common, that everyone should contribute in whatever way they are best able, and that everyone should have what they need, regardless of their position. They also believe that history will inevitably result in a communist system. As feudalism gave way to capitalism, they believe capitalism will give way to socialism and eventually to communism.