Presumably your music files are included within your iTunes Music Library. This material can be synchronised with your iPad. See:
Sync iTunes content on PC with devices on Wi-Fi - Apple Support
Be aware that this is sync-operation - not a transfer. Should you ever need to reset your iPad, you will need to re-sync your Music Library from your Mac to your iPad.
Copying your iTunes Music Library directly to an external storage device is unlikely to be helpful - as the library cannot be directly transferred to your iPad without the aid of a Windows PC (with iTunes for Windows installed) or a Mac computer (with iTunes or Finder - as appropriate for the installed version of macOS).
Similarly, mp3 files copied directly to the iPad without the aid of a suitable computer will not be accessible or playable by the iOS/iPadOS Music App.