Can someone give me a step by step guide on how to fade a piece of music at a particular point (say 3min 08seconds) and then save to play in Clog Amp or similar

Step-by-Step guides to various activities are in the Audacity Manual .

To fade, take your computer mouse and drag-select the region you want to fade. Then use Effect > Fade Out . There are other types of fade out you can use too - have a look around on that page: http://manual.audacityteam.org/o/man/fades.html .

When you want to save an audio file for another application, you have to use File > Export Audio… .