First, be aware that you can do all the obvious things like Bold and Italics, etc., simply by highlighting the text and clicking the appropriate icon.

In addition, you can also add graphics, either linked from a website (you can use an image link) or uploaded (you need to upload the picture first as a file attachment [use the 'files' button at the lower right], then click the Image Wizard). Here's a Dilbert I uploaded, for example:

I did find that it was happier using an image link with a full URL …

You also have the options for bullets, blockquotes, bibliography, equations and even code blocks.

For more info, check the Wiki Syntax help

Hope that helps!

- Rob

Peter