The Moto G5S Plus has a microSD memory card reader. If your personal computer can also read that card type (Most notebooks are so-equipped), you should be able to save music files
The Motorola Moto G5S Plus is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, Zedge and more.
More on free ringtones
Here are links to some of the 100% free ringtones (Motorola Moto G5S Plus-compatible) offered here at MartinsRingtones.com:
Free 'Unclassified' Ringtones Free Tropical Ringtones Free Ringtones-a-gogo Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones