When you use the OfferingTree content editor on your site, you can add images to content by moving to a new line and clicking the "plus" icon. This brings up the "add content" menu. Select the "image" icon.
Next, pick an image you would like to upload from your computer. Your image might take a few seconds to upload during which time you will see and "Uploading Image" message. Once it has been uploaded, you can save your content and view it on your site.