The process is fairly simple, though you need to be careful because some types of audio are protected by copyright. The song should be in an audio format like MP3, AAC, or M4A. You can also upload your own songs or recordings of real-world sounds, if you have them on your computer.
If you want to turn a song into a tonos de llamada, the best place to start is with iTunes. This software is available for Mac and Windows, and it comes with a built-in ringtone maker that allows you to cut out specific portions of the song. If you need to add a little more flexibility to the song, you can even add a loop.
Next, you'll need to set the ringtone's start and stop points. To do this, select a song or audio file in the Library and click the Options tab. Then tick the 'Stop' box to end the song, and 'Start' to start it again. This will ensure that the ringtone plays at the right times, regardless of how fast the song is playing.
Another way to turn a song into a 'ringtone' is to import it directly to iTunes, then cut out the parts you need. This will give you a short snippet that's just long enough to be used as a ringtone, and it won't take up too much space on your phone.
One downside to using this method is that iTunes doesn't automatically save the ringtones to your iPhone. You'll need to sync them with iTunes, or you'll have to transfer them from your computer to your phone by connecting it via a USB cable and clicking 'Trust this Computer' when the message pops up on your screen.