what does the 16g mean

Dialysis man wrote:

What does the + 16 g mean

Do you mean 16GB? If so, that is the total storage capacity of the iPad. However, when you activate the iPad, you will find that you actually have only about 13.8 or 14GB of usable storage space because the iOS and preinstalled apps take up some of the storage already.

The 16, 32 or 64 GB referes to the amount of storage on your device. It's like the size of your hard disk on a computer. That space is used by the operations system (iOS), your apps, and the data they contain. The bigger the number the more stuff your can store on your device.