Cropping and/or Reducing Size

Cropping:

Open a picture.

Click the selection tool.

Select an area. In this case I'm cropping to size 128x128.

Ctrl-c to copy the selection, then Ctrl-v to paste it as a new image.

Reducing Size:

Open a picture.

Shift-s to resize. Use 'smart size'. In this case, I'm reducing it by 50%.

The image is now 96x128.