First of all it remembers what have been in the skeleton the last time this script was invoked.

All files that was removed from the source-skel directory will be removed, restored from backup or ignored.

* It will be ignored if it can not be restored but belongs to a installed
  debian package. It seaches for the file with dpkg -S filename.

* It will be removed it can not be restored and does not belong to a
  debian package. =back

Files that are new in the skel will be installed to the destination directory. And if there are no backup file it will be created.