Chaucer takes advantage of the wide variety of backgrounds to tell an assortment of story styles. The Knight relates a tale of high honour and chivalry (at least as he sees it), whereas the Miller tells a rude, but amusing and clever, story.
All but one of the stories are taken from other sources (the Knight's tale is from Boccaccio, the Reeve's tale is from a fabliaux). The style is usually decasyllabic rhyming couplets. In order to avoid telling a tale, Chaucer (who includes himself as one of the pilgrims) provides a comic moment by telling his story so badly that the host tells him to stop.