Objectivism is a philosophy; it is an integrated set of ideas put forth by Ayn Rand to guide man in living on earth. It is a worldview—an integrated view of existence held by man as the driving force behind his actions. In particular, it is the view that the world is knowable, reason is man’s means of knowing it, and happiness is not only attainable but the proper goal of man living on earth.
The best concretizations of the Objectivist worldview are those portrayed in Ayn Rand’s novels, The Fountainhead and Atlas Shrugged. Aside from the fiction, Ayn Rand wrote voluminously on the subject of Objectivism. Interested readers should look at Philosophy: Who Needs It?, The Virtue of Selfishness, or Capitalism: The Unknown Ideal.
The Ayn Rand Institute’s website contains many great excerpts and summaries of her work. Some good starting points are Introducing Objectivism and The Essentials of Objectivism.