To add an image, first upload it, by clicking Upload File at the lower left menu box, then, go back to the edit view of the article, click the insert image button (embedded file), and replace the example.jpg with the correct filename of the image you just uploaded. Filenames are case sensitive.
- Add |thumb after the filename to make a thumbnail (recommended for large pictures)
- Add |left, right, or center to set the image position on the page
More tips for adjusting the appearance of images can be found here