When you get to the point where you’re reading to look for an agent, I recommend QueryTracker. There is a free option, or subscription for a low annual fee. You can search for agents based on genre criteria and start to put together a list of possible agents. You’ll want to do some research before sending a query, but QueryTracker has easy links to get you to the agency website, blog, Twitter feed, etc.
Once you’ve put together your list, you can use QueryTracker to keep track of whom you’ve sent query letters to, and when, and what the result was, which is really important.
You can find QueryTracker online at https://querytracker.net/