Dear Juddee
Go to the help menu and choose Backup and follow the instructions. You will find " back up family file on FILE" at the top of the page. Usually your file is backed up to a zipped folder, when you close, you can change this to back up to your disc drive, remembering to have the cd in the hole. (Then change it back to legacy Zip, and your hard drive if you want to.) The legacy programme is quite forgiving and you need to experiment to find out what suits you best.
I usually do three back ups of my Legacy file, every month or so, and when I have entered say any significant data. I also back up one report which encapsulates all families, ie multi descendants, and a media back up for photos. Probably there are others who can add to this, but I think you have to sort it out for yourself, and make notes of the procedure, after a while it will become easy.
Do hope this helps, as it is vital you back up your work.
Pat