Upon opening Ringtones, just select Start converting.

Now it will take you to a list of your music library. For our tutorial i will select Linkin Park.

After you select your song it will give you a couple of choices. Quick conversion is easy but it will only take the beginning of the song and make it into a ringtone. We will choose Advanced conversion where you can select where you want your ringtone to start and stop.

Move the cursor to where you want your ringtone to start. Select next when you are done.

Move your cursor again where you want your ringtone to end. Select next when you are done.

Now on the next page select Build Preview.

Now wait while it converts your ringtone. It might take a couple of minutes.

When it is done it will let you preview the ringtone. If you like it, just select Sounds good, Convert it! When that is done just go to your iphone sounds settings and your new ringtone is there.