Question: how to make an mp3 file your ringtone?
Answer: Step 1: Select MP3 Song from iTunes. Open iTunes and select target MP3 music file from My Music or Playlists. ... 
Step 2: Trim MP3 File for Making Ringtone. ... 
Step 3: Select AAC Encoder from Import Settings. ... 
Step 4: Rename AAC File to M4R Ringtone Format.