Check out this great article “What Is a Literary Journal? And How Do I Get Into One?” by friend and fellow poet E. Kristin Anderson. You read more about her on her lovely, informative blog here: Write All the Words!
This article not only gives a short explanation of what a literary journal is, but also gives a bit of history, describes the different types, and how to get started submitting your work. E.K. also gives great advice how to handle rejections.
You may also want to check out these submission related blog posts:
Click here for Aerogramme Writers' Studio article: How to Submit Your Writing to Literary Magazines.