When you make a post, there should be a field labeled "attach" and a button that reads "browse". Hit the browse and navigate to the image, When you are done with your post, click on the bottom "post" button (or "save" if you are editing) The image should appear at the bottom.

If you want to embed an image on a different site click the picture icon (3rd button from the top left) and then enter the URL.

Let me know if you are experiencing any errors.