Step 0: Free download iPhone Ringtone Maker, install and run it.
Step 1: Click the "Browse" button right beside "Input File" label to select the file you want to create ringtone in the window that pops up, then click "OK" button. You will see the file path and name are displayed in the "Input File" textbox.
Step 2: Click "Play" button to hear the music before creating ringtone and find the part you want to use. Then drag and drop the start & end slider to get music clip to convert, or type the start & end time in the corresponding text box directly.
Step 3: Set output destination by clicking "Browse" button on the right side of the "Local Output File" label.
Step 4: If you want, check "Export to iPhone" option to let the program upload the output ringtone to your iPhone directly after conversion.
Step 5: After all above are finished, click "Generate" button to start creating your own iPhone ringtone. During the creation, you can check the process by the progress bar at the bottom.