If I'm not mistaken, that's an iPod nano.
Rather than a user's manual for the iPod, you need to know how to use either iTunes (Windows PCs and older Macs) or Finder (newer Mac OS), although there is no manual for either. However, we can help with that.
Briefly:
- if using iTunes, add music to your iTunes library on your computer, then synchronise the music to the iPod
- if using Mac, use Finder on the Mac to add music to the iPod
- Note that you cannot add music obtained via the Apple Music subscription service to an iPod nano. You can only add music that you have purchased, either from the iTunes Store, other online retailers such as Amazon or Bandcamp, or copied from a CD (compact disc). (You can also add music that you have created and recorded.)
If you let us know whether you have a Mac or a Windows PC, we can provide the steps required to add your music to the iPod.