Google Earth lacks the multiple destination feature found in Google Maps. You can still create and view directions for multiple destinations by saving each generated route and viewing them at the same time. Google Maps can also generate and save directions to multiple destinations as a KML file, which Google Earth can import.
In Google Earth
Get directions to a single destination by clicking the "Directions" tab in Google Earth, providing "From" and "To" addresses and clicking the "Begin Search" button. The directions appear in the list; drag and drop the folder of directions to the "Places" pane beneath the list. Get directions to a second destination by searching for directions again, using the first destination as your "From" address and the second destination as your "To" address. Drag and drop the second set of directions to the "Places" box. Multiple sets of directions can appear on the map at the same time; show or hide them by clicking the check boxes to the left of each folder in the Places pane.
Using Google Maps
Google Maps supports multiple destinations, and you can import the resulting directions into Google Earth. Go to the Google Maps website and click "Get Directions." Provide your origin and destination addresses; click "Add Destination" to add additional destinations. You can click the "By Car," "By Public Transit," "Walking" or "Bicycling" icons to get directions for different modes of transportation; Google Earth only gives driving directions.
Exporting From Google Maps
Click the "Get Directions" button to get your directions, scroll down in the left pane and click "Save to My Maps." Save the directions to an existing map or a new map. Click the "My Places" button at the top of the page and click the name of the map you saved your directions to. Download the directions to your computer as a KML file by clicking the "KML" link beneath the map's name on the map's page.
Importing into Google Earth
Import the downloaded directions into Google Earth by clicking the "File" menu in Google Earth, clicking "Open" and double-clicking the downloaded ".KML" file on your computer. The directions appear in their own folder in the Places pane under the search pane at the left side of the Google Earth window. Click the check boxes to the left of different items in the Places pane to show or hide them on the map.