If you're about ready to start submitting your story into the market, then you need a good resource to get started. Some of these you can look up online, and some you have to pay for.
In my personal experience, usually you pay to save some time with research, but there are times when research actually gives you info you couldn't get by taking the short cut.
Writers Market, from Writers Digest, is one source I like.
It comes out yearly and offers a lot of markets for your work. Of course, I did have an incident a while ago where one of the people in the book I submitted to turned out to be a scam. But with online resources such as http://pred-ed.com/ you can cross reference the info and get a better feel of the agent or editor.
In a previous blog post I explain the experience I had with an agent who wanted me to pay to have them edit and such. These types of agents end up lackadaisically submitting your work and are allowed through contract to hold your work up for up to a year--depending on what's in the contract.
There are other online resources, depending on the genre you are looking to enter. Science Fiction and Fantasy, and Horror is usually thrown somewhere in there from time to time, have a huge community to draw resources from. The two things I showed you above should have tons of links to other helpful sites. Just be careful, because there are a lot of places out there that prey off of helpless writers who are desperate to get their work published. Especially new writers.