Editing an existing article
You may want to visit the starting a new article topic first.
To edit an existing article find the article and then use the edit tab to get into the edit mode.
Editing is pretty straight forward, just try to keep the format the same as the original author to maintain the "articles look". Make sure and give your self credit for your addition if you want to. You can insert text, add text, etc. just like you would on a regular word processor. Use the preveiw mode to take a look and do any further editing. Just make sure you use the "save" button when you are done to save your work.