Featured images for posts
When displaying multiple posts (e.g. a blog, or a category of posts), you can display an image along with the post’s excerpt, as shown in the screenshot below.
The image associated with each post can be set in the post editing interface. Regardless of the size of the uploaded image, the featured image will be displayed at thumbnail size (150px by 150px).
By default, the feature image will not be shown when viewing the post by itself, but you can change this by using the category configuration tool.
Featured images for pages
On a page, the featured image will be ignored unless it’s large enough to be a banner (at least 1140px wide by 240px tall). If it’s large enough, it will appear as the header banner, for this page only.
Setting a featured image
Find the “Featured Image” tool in right column of the page/post editing interface (shown right). Click the “Set featured image” link. This will launch the media upload interface in a popup window. After uploading a picture, or selecting one from the media library, click the blue “Set featured image” button in the lower right.