The basic underlayer was a chemise. This thin nightgown would be worn at night as well as during the day. Because it was against the body it kept the actual clothes clean from sweat. That way you could wash the chemise regularly and not have to wash your actual dress every day. Think of it like when you wear a turtleneck and a wool sweater. At the end of the day you would wash the turtleneck, but you would not wash the wool sweater after every wearing. If you wear a tshirt under a jacket, you would toss the tshirt into the washing machine but just hang the jacket on a hook again. The same is true for medieval outfits. The inner layer would be washed, while the other layer would be reused multiple days before it had to be washed.
The chemise was generally not meant to be seen, especially in colder months. It was underwear. There would always be an over-dress with a floor-length hem on top of that. Perhaps a glimpse of the chemise would show at the neckline or at the end-of-sleeve area. In hotter months the chemise might be more visible as the outer dress had short sleeves or no sleeves.
Men would typically wear a tunic over leggings. Men working in summer heat would sometimes wear simple linen "shorts" without anything else. Their chest and lower legs would be bare. This is a stark difference from how covered up women would be.
Both sexes would wear boots or shoes. There as no "left" or "right" - both halves would be made in the same oval shape.
Cloaks would be worn when going out into poor weather, to help keep you warm. These cloaks could be quite heavy if they were full circle cloaks, and incredibly warm.
Monks would wear similar clothing to non-religious men, but the monk's hair would be cut short and have a "tonsure" - or bald spot - shaved out of its center. The tonsure was a sign of their humility. This illuminated image is from a 12th century manuscript at the library at Cambridge University.
For more specific details on a women's medieval outfit, read:
Women's Medieval Clothing
Medieval Clothing Dyes
Medieval Romance Basics
Medieval Romance for Villagers
Medieval Romance for Nobles
Medieval Romance for Men
Medieval Romance for Women
Life in Medieval Days
Lisa's Medieval Romances
Seeking the Truth
A Sense of Duty
Online Literary Magazines
Lisa Shea's Homepage