The Our Impact page on your website is setup as a blog page. You can read more about how to manage blog posts here.
Any blog post tagged with "featured story" will show up in the Featured Stories section of your website's sidebar. Note that tags are case-sensitive. You can also upload a custom thumbnail image to display in the sidebar. Simply attach an image named "thumbnail.jpg" to the post page under the Files tab. The image should be 232px wide by 150px tall.