juliagray
The first thing to remember is that files on the IIGS are in PRODOS. You will need a program called Passport or Apple File Exchange to translate the files to something that a G3 will read. Here is the process: The 3.5 disks will go into an old SE, Mac LC or other cheap early mac. Those machined usually had Apple File Exchange. The 3.5 disk will go into a G3 but the biggest problem that you may find is that older floppy drives do not always read disks that were not created by that drive.
We can put a floppy disk into five different computers and only one or two will read the disk. The best method is to format a disk in the machine that you are moving files to. Then put the disk into the machine that you are moving the files from. If the disk is recognized, then copy files onto the disk and the newer machine should read the files. Keep trying disks and formatting until one combination works.
Here is a site that gives good information on different drives.
http://vintagemacworld.com/drives.html
If you can post back with the name of a large city near you we might be able to find you a user group that has resources.
Ji~m