To fade out audio in Premiere Pro you can do 2 things. Either applying a 'constant power' transition from the according audio transition effects folder in the 'Effects' panel.

Or you can do it manually by adding keyframes with the pen tool. You don't have to switch to the pen tool, when holding the CTRL/CMD key while hovering over the volume line on the audio clip the cursor will switch to the pen tool and you can add keyframes to the volume.

That's what I use a lot for my tutorials as well because a linear fade out doesn't always work and sometimes you need a little bit more control over the fade out.