1) Navigate to the page you'd like to insert the image.
2) Ensure that you're in the Edit mode of the page by clicking on the pencil icon.
3) Place the cursor in the area you'd like to insert the image.
4) You can insert an image by clicking on the image icon in the Attachment tooltip which should appear on the left-side of the cursor.
5) Alternately, you can also drag-and-drop an image from your external folder into a page which should trigger the upload immediately.