Computer Hope

Hi everyone

How to make iphone ringtone music from iTunes? On the internet they say to select 30 seconds of the music then right click and convert pp stuff but i don't get that when i right click i also tried to crop the music to 30 seconds and drag it to itunes and the cropped music doesn't even show up on itunes.
If anyone knows how to fix this, please tell me how to fix it.
Thank!