What positions are there in a fashion magazine?

This differs by magazine, but in generally there are the following categories of people:

Editors: editors set the overall look and feel of the magazine, as well as content. they communicate with the art director and make final decisions on things like cover

Art Director: they oversee how everything is designed--layouts, images, illustrations, text, covers...and tells those working under him/her (stylists, photographers) how something should look.

Writers: writers generate the content of the magazine--they interview designers, write reviews of new clothing/accessories lines, do on-the-spot critiques at runway events, and predict up and coming trends for the future.

Photographer: photographers may work for many different magazines or just one magazine. The photographer works with the art directors, models, and stylists to shoot fashion spreads.

Stylist: stylists design sets and organize photo shoots. They also help in layouts and the overall look of photo sessions.

A few other positions within fashion magazines are:
- Ad Sales Team: Sells ad space within the publication to brands, retailers, and other companies relevant to their readership. Additionally, they'll work to get sponsorship (money, beverages, gift bag additions, donations, etc) for any events thrown by the magazine.
- Social Media Team: They manage the messaging the voice of the magazine on Twitter, Facebook, Instagram, Pinterest, Tumblr, Vine, Snapette, Google +, YouTube, blog, etc.
- Online Media Team: They oversee content on the magazine online site which at larger publications like InStyle, Marie Clarie, etc is kept separate from the content in the physical magazine.

There are also amazing internships and assistant positions. This can be great to break into the fashion industry, whether it be with a designer or a magazine. Also, there are great 2 year rotational programs in fashion merchandising, which you can start looking at in college (TJX , Macy's and Abercrombie & Fitch come to mind).