How does one go about getting something published in High School?

I’ve been mulling over the idea of sitting down and actually making an attempt to write something worth publishing (as opposed to the random ideas and poems I’ve got scattered around note cards in my room and in the margins of my journal). Well, that being the first step, writing a short story, poem, etc, what would be the second? What steps would I need to take to get myself known? Should I make a website and post it on that or use something like deviantART to get a sort of basis. How do I know if anything I write is even worth publishing in the first place? This is mainly a hypothetical question, but I am curious to know.