The most important thing are accurate GPS coordinates. The GPS coordinates for the position of a mill, you can easily read in google earth. First, make sure that the coordinates are set to decimal degrees. Click on "Tools", "3D-View" and then select the parameter "decimal degrees". Now you can close the Preferences window. Zoom now as close to the mill and place a placemark on the mill. In the window you can now read the longitude and latitude. Copy these values without the ° (degree) sign and add them each in a separate table cell in the table similar to the sample excel files. Depending on which country the mill is, the degrees can get negative values, in this case it's absolutely important to copy the "-" sign!
If you already have an extensive list of coordinates as KMZ or KML file, please send an email so we can discuss whether we can import the data easily from there. If every mill in the file has a name then it is relatively easy.