A KMZ file is a compressed KML file and is easy to make.
- Create a compressed or Zip folder in Windows Explorer (right click > New > Compressed (zipped) folder).
- Open the Zip file, which appears as a folder.
- Drag the KML file into the Zip file/folder.
- Rename the file to have a .kmz extension, rather than the .zip extension that it was given to it by Windows. You can open this KMZ file in Google Earth.
Google Earth Tutorial: Packaging Content in a KMZ File