First you will need to open your iTunes player. I used iTunes because it makes it very easy to drag and drop files. Then, find the song that you want to make a ringtone with. I used Seed 2.0 by The Roots because it is a completely, utterly, badass song.
Step 2: Making your Garageband File
Next, open up Garageband. I'm sure you can use other audio editing software, but Garageband is probably the quickest and most user friendly. Select "Create a New Project." Then name your project (preferably the name of the song you're converting) and click "Create."
Step 3: Delete Default Track and Add New Track
GB will automatically create a default track for a piano. This won't work for importing the song, so go to "Track" in the toolbar and select "Delete Track." Then select "Track" and "New Track" and click "Create" in the selection window.
Step 4: Drag and Drop Song FIle
This is where the magic happens, baby. Go back to iT, reduce the window size enough so you can still see your song in the playlist area, but also so you can see GB behind the iT window. Click and hold the mouse on the song from iT, drag it over to the new track you just made in GB, then drop. (then make sure after the song imports, you drag the wave file back the beginning of the track, which is measure 1.)