Making a career out of writing is serious work. Like any business, it takes research: how to improve the craft, how to break into it, how to get paid, etc. The internet is a great resource. At the same time, it can take insane amounts of time to gather all of that together yourself. Plus, with little or no experience, it can be really hard to know how accurate each site is (especially for the business end).
The great thing about literary and writing magazines is that they have gathered that information for you and put it all in one place. They’re writing especially for aspiring authors, so they’re going to cover a variety of topics you want to know about. Even better, they get articles and interviews with people who are actually in the business (authors, agents, and editors, oh my!), which gives a variety of perspectives from sources that you know have actual experience. And you’re usually told exactly what that experience is in the article.
So should you go and sign yourself up for a bunch of literary magazines right now?
Maybe, maybe not. That is completely up to you. What I would recommend is to go to a library or a book store and check out the magazine in person. If you like to read online, go to their website. See whether you like the layout. See whether they focus on genres you’re interested in. Get a feeling for what it’s like. One reason that there are so many magazine options is that there are so many different kinds of writers. You want to make sure you pick one that works for you.