Bernice: You should have a key on your keyboard normally to the right of the F12 key that says Print Screen....
Once you have pushed that button it will store a picture of whats on your screen. If i remember rightly in XP you will then have to open Paint or a similar program and Paste it into there, then you can save.
Just in case you didnt know XP is long out of date now & Microsoft do not provide any backup or support for it