This is the story of an artist, a painter of icons, and you will see the original icons in all their glory at the end of the film in a full color coda to the story. The artist lives in Russia, which is a vast, often swampy, land with bitter weather. The people, in this film, are clustered in islands of human society where people seem to have made a stand against the land and the weather. Between these islands there is very little and you can see what I mean in the second sequence of the film in which an obviously drafty barn serves as a shelter for dozens of peasants, monks, and entertainers. Outside there is nothing much until a handful of soldiers shows up to drag away one of the entertainers for no obvious reason, disappearing again into the winter pausing only to smash the jester's psaltery.
We then meet and actually start to get to know the protagonist, Rublev in the third sequence, some twenty minutes into the story. We meet him at a monastery, which is another island in the landscape. At this monastery we also meet a Greek painter of icons who is also ah historical figure who will show up with his paintings on a Google search. At this point the story settles down and begins to unfold over the next three hours.
Toward the end the film becomes a project film about the casting of a great bell, not in a factory but in the open with the work taking place with make shift equipment and a terrified overseer. He is afraid because, as is made perfectly clear in the film, he really knows very little about bell making and bragged his way into the job claiming to have inherited secrets from his father. The film ends with one of those long tracking shots for which Tarkovsky is justly famous.
One might mention parenthetically that it appears that Tarkovsky's reputation for tracking shots made such shots a part of Russian films and culminated in a film called The Russian Ark, which is one long uninterrupted tracking (and wandering) shot of the Hermitage museum in Saint Petersburg (Leningrad) where we have a tale woven of the palace and the residents as seen by an unidentified time traveler.
At the end the screen floods with color and the icons themselves appear, not as a part of the story so much as an instructive historical footnote. The rest of the film is in black and white with, it seems to me, a sort of film noir approach to fifteenth century Russia.