Your Moto Z3 features a microSD memory card slot. If your personal computer has a slot for that type of card (Most laptop computers are so-equipped), you should be able to save music files
The Motorola Moto Z3 is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, Myxer and more.
Here is a sample of the free ringtones (Motorola Moto Z3-compatible) offered here at MartinsRingtones.com:
Free Horror MIDI Ringtones Free Ghost Ringtones Free Short Ringtones Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones