Step 1: Getting Started
Now on to the real part. Open up Audacity and select click Project>Import Audio. Or you can just hit Ctrl+I. When the window comes up direct it to the song you wish to use.
Step 2: (Possible) Step 2
Step 3: Shortening (Not vegetable)
Step 4: Exporting
Step 5: The other program: AMR to MP3 converter
Open it up and under the MP3 to AMR tab import any would be ringtones.