Apple discontinued all models of the iPod Nano on July 27, 2017.
The 7th generation iPod nano is distinguished from its predecessors by its larger, multitouch screen, the Lightning connector on the bottom, its thin body, and support for features like Bluetooth audio streaming. The link above takes you to an article that describes the 7th gen. nano in more detail. Once you know if this is the model you've got, you can:
Buy 7th Gen. iPod nano at Amazon.