Audacity is a free, open source, cross-platform audio editor and recorder started by dominic Mazzoni and Roger Dannenberg at Carnegie Mellon University. Audacity can be used for recording, editing, post-processing (normalizing, timming, fading in and out).
Audacity online manual. Includes a great guide to the project window, allowing you to hover over the window, identify the tools and learn how each function works. The website includes also tutorials for specific tasks, from recording, vocal isolation, making ringtones, splitting a recording into separate tracks, and mixing audio tracks.