There are two preference items that may be configured by GeoTag users, although the default values will suffice for most. The Preferences window looks like:

The Make backup files option causes an original copy of the file to be saved — inside of your Trash. If something goes wrong you have a copy of your image before being modified. If all goes well simply empty your Trash to remove the no longer needed unmodified images.

GeoTag uses ExifTool to update images and must know the location of the ExifTool executable file. The default location is /usr/bin/exiftool. That is where the OS X version of ExifTool is typically installed. If using a different version, i.e. from MacPorts, the location can be set by clicking on the exiftool icon and picking Choose... from the pop-up menu or by dragging the location from the finder onto the ExifTool location field. Clicking on the X will reset the path to its default value.