To assign a full article image or intro image, use the images and links tab above the text editor on the article page to upload an image.
Using the Images and links tab, images can be uploaded to the server, or selected from the existing images already stored on the server. Other options on this screen allow the image to be positioned (float) left or right, and alternate text to be assigned. Alternate text is a meaningfull descriptor of the image commonly used by search engines and screen readers to identify the image.
Images can be inserted within the content by using the image icon below the text editor. Position your cursor within the text where you would like your image to appear, and click the image icon to upload new images or select pre-existing images.