If you choose to go the traditional route in publishing your novel, you’re going to need to query an agent.
First off, you’ll need to do your research. Find out which agents are out there, what kinds of stories those agents are looking to represent, and which of the agents looking for a story like yours you’d like to work with.
Next you’ll need to send a query letter to your top picks. It’s basically a cover letter for your story, explaining about yourself and your story and why you’d like that agent to represent it.
If you’re in luck, you’ll get a response. It might be a rejection, if you’re lucky it might be a rejection with some helpful critiques. Or, if you’re extra lucky, it might be a request for a partial or full manuscript. If you don’t hear anything, you can follow up after a reasonable amount of time just to check in and get some closure one way or another before moving on to new queries.
Agents will request partial or full manuscripts depending on their interest. If they requested a partial, they may request a full later if they’re really interested. Unfortunately querying can take ages. You may need to query a number of agents if they aren’t biting, and the response time, especially if agents are reading your full manuscript, can be a bit slower than you may like.
It may also depend on the current market. Agents know which stories will sell in the current market and, even if they love your story, they may know that it’s not one that will sell right now. They may also be representing another story that feels too similar to them to be able to represent both fairly.
If you’re querying, good luck out there.