Once you've registered on the site, this is pretty easy. Make sure you are logged in. Then go to the menu on the left side of the page, and go to Create Content->Story.  Once you've done that, you will go into the story editor.  Put a title in the story.  Select a topic from the menu (or you can select multiple topics by holding down the control key and clicking on multiple topics).  Fill in the body of the article - you'll get a simple editor that will let you do lots of different things like set bold face, italics, etc.  You can even put in a picture, but thats going to be a different page in here. In most cases, that's all you're going to have to do - click on submit at the bottom of the page.  Stories are held for moderation by the editors.  Once it's approved, it will show up on the main page of the web site.