[App_rpt-users] Need help DD command

I recently set-up a BBB. When getting the image from www.hamvoip.net I tried use my new installation of Ubuntu 14.04, mostly because I am trying to learn Linux by just using it. I didn’t have any luck and just to keep the project moving I resorted back to windows to complete the image copy. I would like to learn how to copy a .img file to a micro sd card using DD. I would also like to know how to do the reverse of taking a micro sd card and making a .img file for backup. Is there anyone on the list willing to help me with this? Thank you Bob/N1XBM