Q: How can I make an iTunes song into a ringtone?

http://osxdaily.com/2010/09/04/make-free-iphone-ringtones-in-itunes-10/

https://discussions.apple.com/message/17777381#17777381 - making a ringtone

Note the location of the "convert" feature has changed in iTunes 12.4 to the main file menu.

Make Ringable v1.1 - http://dougscripts.com/475 - Applescript to make a ringtone

Oct. 2010 Getting ringtones folder to show in iTunes - https://discussions.apple.com/message/12496240#12496240 - iTunes > Preferences. Under the General tab below Show, confirm Ringtones is selected

I can't add m4r files to itunes. - https://discussions.apple.com/message/22240099 - largely a matter of people not realizing when you add a file to iTunes it puts a copy of the file in the iTunes folder and uses that, not the original file.

How to sync ringtones to your iPhone - https://discussions.apple.com/docs/DOC-3792   iTunes11 tip: https://discussions.apple.com/message/20573388#20573388

Ringtones location iTune12 - https://discussions.apple.com/message/28351205#28351205

To select a ringtone on the iPhone: Device Settings > Sounds > Ringtone