The Moto G5S features a microSD memory card slot. If your personal computer is compatible with that type of card (Most notebooks are so-equipped), you should be able to save music files
The Motorola Moto G5S is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, Zedge and more.
Here are links to some of the free ringtones (Motorola Moto G5S-compatible) offered here at MartinsRingtones.com:
Free Horror MIDI Ringtones Free Tropical Ringtones Free Ringtones-a-gogo Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones