The operating system (OS) of a device refers to the technology that powers the smartphone or tablet. This is important to know because it tells you which application marketplace to go to download FamilyTime and other apps. In most cases, it's pretty straightforward to know what the OS is: All iPhones, iPads and iPod Touch devices run iOS. There are several manufacturers that offer Android handsets (Samsung, HTC and Motorola are some of the popular ones.) While Amazon Fire Phones and Kindle Fire Tablets run the Amazon Fire OS.
The easiest way to tell what operating system your smartphone or tablets runs is to check the "about us" on the device; check the documentation that came with the device or failing that, do a quick Internet search.