If you'd like to insert an image, video, or audio file, you'll need to first load the file to the page. Click on the button that says "files" located along the bottom right hand corner of the page and upload your image, video, or audio file. Then, when you are editing a page, click on the picture, video, or audio buttons located in the second row of toolbars above the text window.
Be sure to write the name of your file exactly as it appears with the file extension (i.e. .jpg, .gif) where it says "source", or nothing will show up. This is case sensitive.