Select and save as a new photo

The shortest way:

- Your selection is active (marching ants). Shortcut Ctrl J. That puts the selection on a new layer.

- Alt  click on the eye on the left of the new layer in the layer panel. Only the selection is visible.

- Menu File >> duplicate. Tick the checkbox to create a flattened version of the selection.

Now, you have two files opened in the photobin; the original and the selection.

The original shows only the selection layer: alt click again on the eye and all layers are again visible.

Note that the newly created file is not yet saved on your drive. If you want to keep it, save it after editing.