The A3L has a microSD memory card slot. If your personal computer has a slot for that card type (Most notebooks are so-equipped), you should be able to save music files
The NUU A3L 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 (NUU A3L-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