Sharing A Folder
To share a folder like "2011 Insurance Certificates" below left click on the down arrow at the right of the folder. Then click on "Share ..." and "Share ..." again.
You should end up with a dialogue that looks like
In the add people text box you can put a group name (eg email@example.com or firstname.lastname@example.org). You'll also be able to select Edit or View. In addition you'll be able to notify the people that have access if you choose. Press "Done".