When you have finished editing your content - be it story, page or comment there are many options available below the main editor window. You can ignore most of them until you are an experienced user who needs to do more than simply write/preview/edit/submit.
Here is a brief overview of them, with the ones you need to know about highlighted. Any options preceded by an arrow will open up on the page.
[Preview ] [Submit]
I'll look at Preview and Submit here, and deal with Publishing options on the next few pages.
Preview is used to look at your edited article and see what it will look like when it is published. This is a good option to use as it gives you a second chance to review your words and your format and to ensure that you are saying what you want to say as clearly and simply as possible.
If your article is long the preview will show it in two parts: the teaser and the complete article. The teaser is what will show up on the front page, with a link to the complete article. Below the teaser and complete article is the whole editing page again. Continue with the edit/preview cycle until you are ready to submit.
Once you submit your story, it is available for other website users to see.