When someone shares a file or folder with you from their Google Drive, you can add this to your personal "My Drive" section of Google Drive.
Open Google drive and click the link on the left for "Shared with me"
find the file or Folder that you want to add to My Drive and right click
from the pop up menu select Add to My Drive
Go to the MY DRIVE link on the left and the file or folder should now be available.
Doing this makes the file/folder available to sync to your local hard drive using "Back up and Sync" or "File Stream"