Knitting in medieval times was general used for hose, socks, caps, and undershirts. Double pointed needles were the only type known and the knitting was generally done in the round, just like Fair Isle or old Nordic knitting. Usually wooden needles were more common than metal ones. Knitted shirts as an outer garment didn't become popular until the 16th century, when they were knit in silk, cotton, and linen as the dress of the rich.
Medieval Knitting Links
Medieval Knitting Info
Medieval Muslim Knitting
Pattern for Late Elizabethan Stockings
SCA message compilation about period knitting