Taking a screen shot is the best way to save a picture of an app's screen, or of an onscreen error, to send us. On your iPhone or iPad, simultaneously press the on / off switch and the center home button. You will notice an on-screen flash. If you have sound enabled, you will hear a camera click.
The image is saved to your Photo's (icon with the flower on it). From there you can open your photos and send the image by email.