There are a couple of ways
1) Look at the acknowledgments of your favorite books, or do a search to try to find your favorite author's agent. (If that author has written a book that's at least somewhat similar to your own, in terms of genre or audience). Then look that agent up online. Every agent has a website, where you can find information about whether or not they're accepting submissions. It's more likely that you'll have a rapport with an agent whose work you know than one who represents books you've never read
2) Begin your search here http://www.agentquery.com
When you're searching for an agent to submit to, make sure you're doing a lot of research. Don't just start sending your work out, willy nilly. Make sure the agent is someone you'd actually want to work with. Check their twitter feed, their website, their facebook page. It's also a bonus if you've read something they've represented.