Shift+C initiates a crop,
besides clicking on the Crop button below the image
how to Crop to Selection?

Normally you should be able to use the Enter key to trigger the final cropping.

For a while due to a bug this was broken, but since Gwenview version 17.04.2 it should work again.

thanks
enter key brings me to a icon list of all images
16.12.3
also have no way set sort to "Natural Counting"
I'll take it up with my distro...