How do you know where to send it? In submitting, research is extremely important. You have to make sure the publication you are submitting to is a good match for your unique story.
One great resources to use for researching is Duotrope's Digest where you can search for your particular genre, length, etc. While they try to keep up with the latest, you must always follow through to the website of the publisher itself and scour the submission guidelines before you submit.
Another great resource is a current year's Writer's Digest market book. Go to eBay, Amazon, your favorite bookstore, or simply search online to find one. It is definitely worth the investment. Inside these market books are detailed listings that will help you figure out where to submit your story. However, you must always do further research. Writer's Digest market books are published once a year and the publishing industry is constantly changing. Always re-check the listing online to make sure they still want what they stated in the market book.
Following guidelines is extremely important. Don't give them an off the wall reason to reject your work because you didn't follow guidelines. Recheck the word count. Make sure you are sending them your work via their preferred method (some like snail mail over email and vise versa). Recheck how your work is formatted. Make sure that if you are sending it via email whether you need to send it as an attachment or copy/paste in the body of the email. Make sure you know what file to use for the attachment. Make sure you know how to format and where your contact information should go.
And one of the most important things you can do when submitting is... DON'T BE AFRAID. Don't overlook submitting to bigger names just because you think they couldn't possibly want to read it. You never know unless you try. Each submission and rejection is a learning experience and is a step closer to getting published. Don't be afraid to put yourself out there or you'll never succeed.