Like many glam professions, writing is very competitive and actually involves a lot of tough work. Good writers laboriously research and report, then craft every word, writing and re-writing. Most publications print only a fraction of the stories that writers try to sell to them, and publishers reject the vast majority of book proposals. When writers do get gigs, they're often not paid a lot. Or you can write a book and sell it to a publisher.
Many writers learn their craft writing for periodicals, and go on to write books.
If your goal is to work at a magazine you love, it's likely that you'll end up doing more editing than writing. Long feature stories are usually done by freelancers. Getting your BA or MA at a school with a great internship program and alumni with lots of connections will take you a long way toward getting a foothold in this highly competitive field. And freelancers don't have a boss looking over their shoulder. Your connections can get your foot in the door but, if you are mediocre, you may not get successfully published.