Custom Thumbnail Sizes
Creating Different Thumbnail Sizes:
To set a Custom Thumbnail Image Size you just go to Extender Settings > General Settings > Custom Thumbnail Sizes and set the Mode (Resize or Crop) and both the Width and Height for each Custom Thumbnail option. You do not have to set any of them or you can just set one or two. They are only there if you need them.
Once set you will be able to access them through both the Thumbnail Size drop-down menu in any of your Genesis Featured Posts/Page Widgets.
Resize vs Crop:
Both Mode options resize the images, but the Crop option will actually crop your images, if necessary, to ensure your exact image size is obtained. With the Resize option you will retain the aspect ratio of your images, but therefore not see your exact dimensions reached.
If you set a new Custom Thumbnail Size AFTER an image has been uploaded/added to a WordPress Post/Page then you may need to regenerate your thumbnails to have your new Thumbnail Size take effect. You can easily do this with the Regenerate Thumbnails WordPress Plugin.