Editing and applying effects in Audacity is pretty simple but here is a begining look..

Open or record a file and select part or all of it..

In this instrence we are going to Normalize a file from the Effect menu

In this next case we are going to remove noise. Find a quiet part of the sound that is all noise as the end of this file is and select it. Then open Noise Removal from the effect menu. There are two steps first select "get the noise profile" and then afterwward remove noise.

when complete you can Export as MP3 from the file menu.