The title's a bit of a misnomer. It is, to be specific, about the pictorial representation of the months, in calendars but in other forms, too, like Books of Hours.
There was a widely used format (with some widely used variants, as well; more of them in the later centuries than the earlier ones), but the basic structure would show peasants through the year, carrying out tasks in due season. Always the appropriate season -- it would be kinda hard to fool their customers that way -- planting, plowing, harvesting, slaughtering, etc. In ideal circumstances. The peasants are never very handsome, but they are all clearly well-fed and well-dressed. Sometimes in the larger scenes some are taking a break for some well-earned food. And the crops are somewhat limited. Even though these calenders were mostly popular in northern Europe, grapes were one of the commonest images. Along with wheat, hay, and slaughtering animals -- all other sources of food got stinted.
Winter gets a bit interesting as there are fewer appropriate tasks. Slaughtering in December, or baking bread, or threshing grain, sometimes, but often they just showed someone eating and warming himself by a fire.
Springtime sometimes had a garden instead. An enclosed garden, of course; since this was not a time of city living, it was the city and not the countryside that was the ideal. The peasants would usually be digging or pruning rather than any other of the myriad tasks involved, and frequently the master or mistress (or both) would be inspecting it, which is unusual because most of these scenes just have the peasants working alone.
And sometimes you had the sheep let out to pasture. Despite their importance, sheep were rather rare, although sheep-sheering became a standard variation that could, if the artist liked, replace hay-making in June.
Autumn was always harvest -- though sometimes they stuck in barrel-making, too, because you had to store the wine.
Children were rare birds in the pictures -- usually marginalia or side-notes. Apparently they were not part of the working agricultural scene -- at least, not the ideal one.
Women were rare in the earliest images, but grew more common as the centuries worn on. Partly because, perhaps, the images tended to get larger and so had more figures, partly because, perhaps, labor shortages made them more conspicuous. No one quites knows why. Occasionally, they appear spinning, but since spinning, though one of the more time-consuming labors, was not a seasonal task, it didn't have an approved month.
An interesting view on arts, and ideas about agriculture and how they appeared in art..