Hi Ursula,
I second Gene's advice to get a newer camera if you can. In the meantime, with regards to your questions:
1) You can use them as backups, but it's not the best choice of backup media (an external HDD or CD/DVD/Bluray backups are preferred - and always have at least one off-site copy). You can easily format them in the computer. Most cards come preformatted as FAT32 (older) or exFAT (newer) anyway.
2) Do you mean SDXC vs SDHC vs SD? The HC stands for high capacity (whilst XC stands for eXtended Capacity) and is a newer design (although the physical shape and electrlcal characteristics are still the same, so SDXC/SDHC devices can support the older SD cards). From what I can find about your camera, it doesn't support SDXC/SDHC cards; these won't work, I'm afraid.
3) I think what you're referring to here is the SD card "class". This denotes the speed of the card. Many older devices use Class 2 or 4. You can find Class 6, but it's less common. Most new devices can use Class 10 or SD cards that have a new class number - UHS-I or UHS-II (Ultra High Speed) which generally include a transfer rate (30MB/s, 45MB/s, 80MB/s, etc.). UHS is only applicable to some SDHC and SDXC, so if your card is labelled with this, it won't work.
In short, you need to find older SD cards (not SDHC or SDXC) for your camera, or purchase a newer camera.
Hope that helps.
