Export in what way? This program doesn't really modify images directly in any way, so I'm not sure what kind of format you might expect from an export feature.
You can grab individual sprites and use CTRL + C to copy them to the clipboard. From there, you can place them into any graphics program you wish, and export that into any format that your graphics program allows.
That's more or less its intended use - as a sort of companion/helper app for working with specific kinds of spritesheets.