Regenerating images after new image style
Drupal creates derivatives images "on the fly" based on a defined image style. The act of creating a new style does not generate any images. Rather, the first time an image is requested using that style it will be generated and saved in sites/default/files/styles/{stylename}/path/to/image.jpg.

If you (for example) create a view that displays nodes with images using your newly defined image style, then as soon as you go to a page with that view the images will be generated.