What did men and boys wear in the medieval times?

Answer They wear clothe made out of animal skins.  Answer Actually, they didn't wear animal skins much. Nobles wore tunics, breeches, hoses and underclothes, whereas commoners wore rags and anything they could find that would give them warmth and conceal their bodies.  Answer If you think about it, medieval serfs wore mostly clothes they made in their homes, and when these became rags, they were replaced because the people who made them could make more.
Serfs wore tunics rather like those used in ancient Rome, at the beginning. In many northern areas, they added breeches. With the passing of time it was breeches and short tunics, then shirts.
Middle class people wore much the same sort of thing much of the time, but always wanted to appear better off than they were and wanted to look like lords and ladies, so they went in for better clothes. Unfortunately for them, there were sumptuary laws prohibiting them from actually copying the fashions of the nobility, so they could not wear the same fine jewelry, fur lined clothes, or silks.
There is a link below to a related question, "What were medieval fashions like?" and there are links from that to articles on the subject.