It's very easy to use Driving Directions in Google Earth. Practically, the process is the same as in Google Maps. First you have to use a Placemark which will be the starting point and then navigate to the destination and right click it, then choose To Here. At this point, Google Earth will initiate the driving directions module and calculate the path based on your settings. You can drag the path to make it more suitable based on your preferences.
Another way is to use Search to type an address, then switch to the Directions tab to enter the arrival destination: Google Earth will create it for you.
Use the support page provided by Google: https://support.google.com/earth/answer/148083?hl=en
