Symbols are objects, characters, figures, and colors used to represent abstract ideas or concepts.
The books and manuscripts that appear everywhere in Don Quixote symbolize the importance and influence of fiction and literature in everyday life. The books instruct and inform the ignorant and provide an imaginative outlet for characters with otherwise dull lives.
Horses symbolize movement and status in the novel and often denote a character’s worth or class. The pilgrims outside Barcelona, for instance, walk to the city. The noblemen ride in carriages, and the robbers and Don Quixote ride on horseback. In Don Quixote’s mind, at least, the appearance of horses on the horizon symbolizes the coming of a new adventure. Indeed, Rocinante and Dapple play an important role in the journeys of Don Quixote and Sancho; they are not only means of transport and symbols of status but also companions.
The inns that appear throughout the novel are meeting places for people of all classes. They are the only locations in the novel where ordinarily segregated individuals speak and exchange stories. Inns symbolize rest and food but also corruption and greed, since many innkeepers in the novel are devious. Sancho often longs to stay at an inn rather than follow Don Quixote’s chivalric desire to sleep under the stars. These opposing preferences show Sancho’s connection with reality and society and his instinctive desire for comfort, in contrast to Don Quixote’s alienation from society and its norms. Even when he does stay at inns, Don Quixote is noticeably alienated from the major events that take place there, such as the reunification of the four lovers in the First Part.
Source: http://www.sparknotes.com/lit/donquixote/themes.html
Next Reading: Chapter 1