yep, you're question isn't the clearest!
However...
if you're going to print something, you generally use the dimensions of the paper to determine pixels dimensions of your image. Say you want to print a 6x4" then pick/determine the resolution you want (say 300dpi) and multiple that by your print dimension, so in this case you'd have 1800x1200 pixels. Crop/resize your image to that and your 6x4 should come out sometwhat similar... I say somewhat because I've found that the printing machines seem to crop a bit more off. I actually use 1812x1208 pixels for a 6x4" (allowing a little extra room around the important aspects of the image.. eg peoples heads) and get back a print that represents what a 1800x1200 image should give.
If you're get prints done commericially you might ask them if any extra is cropped. Printing yourself then just work on the W x desired resolution & H x Desired resolution formula to size to the paper.
Hope that is relevant to what you're asking.
Cheers, Nige