Research your genre. Most writers have a well-worn stack of their favorite novels next to their bed, but it's important to be familiar with the current trends in the fantasy genre. Go to the bookstore to get a feel for what sorts of novels are selling well, and who is publishing them. Check the author's acknowledgments for mentions of agents and editors who may be interested in your novel.
Go to agentquery.com or writersmarket.com to find agents who specialize in the fantasy genre. Queries can be submitted directly to editors of most small presses and some larger publishing houses, but an agent can be a powerful ally when you're navigating the perils of the publishing world. They only get paid when you get paid, so your fates are tied together.
Write an entrancing query letter. This is possibly the most important bit of writing you'll ever create, so make certain it shines. Introduce yourself, then hook the agent with a paragraph or two about your story that reads like the back flap of your favorite fantasy novel. Don't ramble on about your story, your characters, or the fantasy world you've created; leave the agent wanting to read more.
Format your query letter like the business letter it is and print it out on plain white paper, single-spaced using 12-point Times New Roman font. Any sample pages from your novel should be double spaced, but keep the plain white paper with 12-point Times New Roman font.
Begin submitting your query letter to agents, making sure to follow each one's submission guidelines. Include a self-addressed stamped envelope with your submissions so agents can mail you their response. Most authors are rejected several times before they publish a book; if you receive a rejection keep writing, keep learning, keep submitting, and never give up. The main difference between many published and unpublished writers is tenacity.