A.) Write a story.
B.) Revise the hell out of it. Like twenty times. Revise like a poet. Test every word to make sure it is needed.
C.) Review places that are looking for new authors. Start with local publications, school magazines, or online only journals. Duotrope.com is an excellent service to sign up for. They tell you want kind of stories each place accepts, and at what level of writer. You want to read some of the journals to see where your work would fit in. You want to find people that like writing like yours. Create a spreadsheet to track your research.
If you don't want to pay for Duotrope, review these links:
D.) Write a query letter. Use a formal letter format. Find out the editor's name. Describe your story in a single sentence with word count. Tell why you are sending it to that publication. Have a brief paragraph stating any other publications you have and your educational background. Nothing else. Do not tell them that you have been writing since you were nine. Be professional. Less is more; the whole goal of the letter is to get them to read your story. Thank them for their time.
E.) Follow the journal's directions for submittal to the letter. Do they want email? Submittable? Snail mail? Do exactly what they say.
F.) Send out to about 10-20 magazines and journals at a time. Create a spreadsheet to keep track of where you have sent them. Start with those magazines that might be a little out of your reach. After about six months, send to the next round of magazines--aiming a little lower. Again, keep track. Repeat.
G.) Wait. Don't pester anyone. Just wait.
H.) When you do get accepted, send a note to anyone still reviewing your story alerting them that you found a home for the story somewhere else. Thank them for their time. Be nice.