iPhones only take ringtones as M4R files of up to 40 seconds. Add a song, select the chorus on the waveform (the selection won't go past the limit) and hit “Make ringtone”. For Android, choose MP3 or OGG and go up to 60 seconds.
Fade in and fade out are already on, so the ring doesn't start with a bang or cut off mid-word. Quiet song? Turn up the volume slider.
Step-by-step install instructions appear under the result. No song in mind? The AI can compose an original ringtone melody for 13 credits, and the editor picks up from there.