The Galaxy On Nxt features a microSD memory card reader. If your personal computer can also read that type of card (Most notebooks are so-equipped), you should be able to save music files
The Samsung Galaxy On Nxt 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 (Samsung Galaxy On Nxt-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