To export your tracks to Google Earth you will need to have Google Earth installed.
Go to the History page and select the flights that you would like to view. You can select multiple flights at a time or if you would like to all visible flights, simply click on the select all box at the top left. Note, this will only select the current flights that are loaded. To load more flights scroll down to the bottom of the page.
If you have a specific date range, enter the date range through the time selection button.
Once you have selected a flight you will be able to download a file of the flight. To display in Google Earth you will need to download a KML file.
Click on the download icon at the top of the page and select KML. Please note that if you are trying to download a large number of flights into one KML file the website may timeout. You may need to do multiple exports.