if someone wanted to submit one of their writings, poems, or works of art into a magazine for instance, Seventeen, How would they do so?

This might save you some trouble. You should write a 'query letter' to the magazine, describing the article you would like to write and why you think you're the best person to write such an article. If you have ideas for photos to accompany the article, or ideas about why readers would want to read such an article at this time (i.e. they're putting together the winter issues now, so if your article is about skating, for example, it's timely) mention this too. Letter should be one page long. You can enclose a 1-page resume, too, if you want to.

Then, if they might want such an article, they will contact you. If not, you save time, paper and postage.