The Firm Under Perfect Competition

Our experiences tell us that for every product we buy there is at least one product that can always substitute for it, although in some cases these products may not be the best substitutes available. At any rate, firms supplying these competing commodities are said to be in what we call competition. And so if there are many products of similar features and are perceived to be equally satisfactory by the buyers, then each is a good substitute for the other. These firms competing are in perfect competition.

How does a firm behave given that the industry he is participating in operates under perfect competition? You can figure it out if you open the following links:
http://www.amosweb.com/cgi-bin/awb_nav.pl?s=wpd&c=dsp&k=perfect+competition
Be sure to understand the structure characterizing the perfect market. What motivates the firm to produce?How does the idea of marginal cost link with supply?
http://www.econmodel.com/classic/ucost1.htm
What is the theory behind production when the market is perfect? What are the assumptions behind the model for the theory to work?
http://www.tutor2u.net/economics/content/topics/monopoly/perfect_competition.htm
http://www.clas.ufl.edu/users/rjohnson/Graduate_Policy_Analysis/perfectcompetition.html
http://answers.yahoo.com/question/index?qid=20061116144354AAvWrS3
http://cepa.newschool.edu/het/essays/product/profit.htm