Without a doubt the best application if you are doing any kind of audio recording or editing. (but NCH's Wavepad is simple and free too )

Audacity is open source and download here. It allows you to edit, mix, record, convert audio files. Invaluable. I've used it over the years and with guidance, really easy for students to pick up and manage.  The only tricky thing is that you must have the Lame encoder to make your files into mp3

Russell Stannard just made a great, complete tutorial on how get and use! Also see the Audacity Wiki for help/info. Here too is another tutorial you might like. Get recording! Get podcasting and sharing mp3 recordings online and off.