Files you put in your My Drive in the Google Drive web interface will automatically be downloaded to the Google Drive folder. When you install Google Drive for Mac/PC it adds a folder called ‘Google Drive’ to your computer.
The Google Drive for Mac/PC tool allows you to synchronise either all the contents of your My Drive, or just selected folders. If you’re like me and store all your files in Google Drive, it can be really convenient to synchronise them to your computer. Please see this newer blog post for information on how to install and use it.** **UPDATE: The Google Drive for Mac/PC tool has been replaced by Google Backup and Sync.