Just some tips that, i hope, could help (never published anything myself):
-if you want to submit a novel to a "major" magazine:
- Inlcude at least 50% of the work. They will not hire you just by the first chapter, however good it is.
- Be sure the format of each chapter fits with the format the magazine's editor wants. That's very important! For that, analyze the work of the other contributors for the magazine. Even better, ask one of the contributors: find its email, or ask the magazine to get in touch with one of them you like.
-Sometime, it's needed to have a heavy-weight Curriculum Vitae to get a chance. Editors don't recognize talent, they recognize success. So you might want to find a local fan-zine, with lower reach but more openness. There are a lot of litteracy circles around editing their own short-stories. Try to find them. Or even, start your own zine with ppl you know. You might even get funds from your school if you do it.
-Keep on! If it fails the first time, don't despair. Try other magazines, try them all. And most of all, continue writing!
Perseverance is the most rewarding virtue.
Good luck!