Finish your book. (can't emphasize that enough) Revise and edit until it is as close to perfection as it will ever get.
Write a query letter and a synopsis. Go here to learn how to write those. The password is vista.
http://www.absolutewrite.com/forums/forumdisplay.php?f=174 The how-to threads are at the very top of the list.
Revise and edit until they are perfect. Don't think you're special and write a four page query letter.
One page means one page.
Go to Agent Query for example and get a list of agents who represent what you have written. No point sending a thriller to an agent who represents romance. Check each agent at preditors and editors.
http://anotherealm.com/prededitors/
There are a lot of scam agents. If any agent asks for money to read your novel or to represent your novel he is a scam artist. An agent collects his percentage from your sale. He gets no money until you get paid. Ever. Ever. Ever. Under no circumstances. Ever.
Send the agent exactly what he asks for. No more, no less. Don't think you're special and send him the entire novel.
It's usually a good idea to send to about ten or fifteen agents at a time. If you are very lucky, an agent might respond with a personal note about how to make your book better. If you've sent to every agent, you'll have no one to send the new and improved book to.
Wait. A long time. Two to three months is an average response time and some may never respond at all.
All of this information could have been found using the search feature on AbsoluteWrite and on Google. Search is your friend. Use it.
Welcome to the boards. Tons of good information here. Uncle Jim's thread in the Novel Forum is especially great. Don't forget to check the sticky threads at the top of each forum list. Those are especially useful.
Good luck.