3. Step 1: creating a recording
If you have iTunes, you can use iTunes to convert the recording to the MP3 format. iTunes is available for Mac OS X and Windows.
Instead, you may want to consider using Audacity. This is an audio editor and recorder that is available for Linux, Mac OS X and Windows. It can be used to make recordings, edit an existing recording (e.g., to remove any unwanted sections at the start and the end), or to convert a recording to MP3.