If you would like to show your post in homepage slider (showcase), you need to add 2 custom fields while you publishing it. First is showcase_image, which you set the image to show, and the second one is showcase_color to set the background color of the showcase for this item.

First upload your picture by using Upload / Insert option of wordpress, or via FTP Client, then get the full path of the image. Use this image path as a value of showcase_image named custom field, and click on Add Custom Field button. Later, add showcase_color named custom field with the color code value. Enter the color code value without using # sign like CC0000

NOTICE : To make homepage slider (showcase) working, you need to publish 2 posts at least.