The Writer's Market has a great list of literary agents, which is your first step.

Do not send chapters to an agent until they ask for them! You must first write a query letter, explaining what your book is about, if it is a stand alone novel or if it will be a series, etc. Keep it concise, agents have to read alot.

Plan on several rejections. Once an agent is interested, he or she will ask for the first chapter or the first three chapters. If the agent likes those, he or she will ask for the remainder of the novel. If the agent likes the book, he'll then try to market it to a publisher.

Author Stephanie Meyer talks about this process in length on her website: www.stephaniemeyer.com