download ringtone maker from app store.
then load app and pick what song you want.
the app lets you pick what part of the song you want (can only do 30 seconds unless you upgrade to the pro feature for 40 seconds for $1.99)
then go to the apps tab on your iphone in itunes
scroll to bottom to the file sharing section
click ringtone maker
click the song you made
click save to (i chose desktop)
click n drag song from desktop into top left section of itunes
ringtones icon shows up
on iphone go to settings>sounds>ringtone>then it will show a list of custom ones you made.
Sounds hard but after you do one or two it is easy. you can also watch youtube video on how to use it.