Ah, publications. They are not as big a deal as they once were. Medium has shifted its focus to individual writers. However, as a newbie, it's a good idea to become known on a few publications and publish there regularly. Before submitting, read each publications' guidelines. Most require you to use a picture under the headline. Some like your subhead in subhead font and others in plain sentence. Pretty much everyone insists an image you use cites the source. You can get copyright free ones from Unsplash which is built in to Medium's software. Learn about story tags as this has become more important to story distribution than it used to be.