XMP files are tiny data files of about 8kb each which can be created by Adobe Photoshop or Lightroom. They hold all of the raw processing settings, as well as star ratings, colour labels, and so forth.
Sending XMP files over the internet is a very fast way of returning the corrected files. You send us raw files by FTP or post, and the resulting XMP files can be returned by FTP as a tiny download, saving a postal delay of a few days.
Once you receive the XMP files, you unzip the zipped file which contains them all (by double clicking) and copy them into your folder of related raw files. Then, following the instructions provided, Adobe Bridge or Lightroom can read the settings, and the conversion to jpeg runs on your computer using the settings provided.
We just need to know which version of Photoshop or Lightroom you’re using.