I talk a lot about compression because it is such an excellent audio editing tool. But it’s very powerful and so capable of big changes in your audio, including making it (the audio) sound really bad. So it’s important to understand what compression does and at least the basics of how it works. Here are a few of my articles on compression – Improve Or Ruin Your Audio With an Effect Called Compression and Vocal Compression Using Reaper’s ReaComp Effect Plugin.
I just ran across a pretty comprehensive, if a tad technical, article that covers all of those compression basics: