Question: how do you make an itunes song into a ringtone with garageband?
Answer: Open GarageBand on your iPhone, iPad or iPod touch.
In the My Songs browser, tap Browse. , tap Select, then tap the project you shared from your Mac.
Tap. ... 
Enter a name for the ringtone, then tap Export. ... 
Tap Export.
When the ringtone is finished exporting, you can assign the ringtone.