If you are interested in creating a multimedia project involving audio and video, there are a couple sites you may want to visit. Each of these sites has information on how to set-up, shoot and compose your photos, videos and audio.
Media College - http://www.mediacollege.com/ - This site features tutorials on photography, video, audio, lighting and more. Click on the links located in the upper right corner of the main page to find tutorials on various subjects.
CNN iReport - http://ireport.cnn.com/toolkit.jspa - This site provides tips for storytelling, taking photos, recording video and recording audio.
Audacity is a free, open-source audio editor and is compatible on Mac, Windows, and Linux. It is a full-featured audio editor that allows you to record, mix, edit and create any project you need or desire to. There are many tutorials and helps online. Audacity will not automatically export 'mp3' files. In order to be able to do this, you will need to download and install another file called LAME. You will only need to do this once. There are instructions on the site how to do this. Some screen shots of the program are below.
This is the main Audacity window.
These are the main controls in Audacity.
These are the main tools in Audacity
GarageBand is Apples audio editor. It is a part of the iLife suite of applications including iTunes, iPhoto, and iMovie. It is a Mac only program. It works similarly to Audacity for recording, editing and mixing. One difference is that GarageBand has a library of sounds and "jingles" that you can include in your projects. It integrates with iTunes, and iPhoto to pull in music and images into your project. Some screen shots are below (CTRL or Cmd click on an image to see a larger version in another tab).
This is the "Chooser". It allows you to pick the type of project you are going to create.