I'm just getting started and I had several 12 x 12 pages printed at Costco. One was missing 1/2" of the page on one side and the lady in the photo lab said I have to allow a 20 pixel "bleed" area around the layout. She said that is what the scrapbookers that print there do.

Anyone know what that means and how you do that in Photoshop Elements 10?

Also when I compared them carefully I noticed that
one page was missing about 1/4" from all four sides,
one was missing about 1/2 an inch on the right only
and one was missing well over 1/2 an inch on both sides (sorry I am not good with inches so don't have exact - all those 1/8's 1/16's etc just seem so confusing but didn't think people were used to centimetres :-).

Why would they all be different? The photo lady said she just prints them as they come.
And I really need help with the 20 pixel bleed area. Thanks