Sheila, all you have to do is open up the one you want to use, and then highlight it by right clicking just outside the top left corner and drag your cursor all the way to the bottom right hand corner. When the entire background is highlighted, just click on the copy icon at the top of a new message box where you're wanting to use it, and after the msg box loads, just hit the paste icon...and it should appear.
If you need more help, just let me know.
Hugs,
Cathy