Sound engineers take really sterile tracks and make them sound natural through audio effects. The most common tools to do this are delay/echo and reverb, and with some know-how you can tweak your own tracks for the better. All of these effects work to help make audio sound better, deeper, and more natural. They’re also used as aesthetic effects, too, and understanding how they work will help you use them to their utmost potential. You can find them all under the Effects menu of Audacity.