Fading audio / music in and out and creating audio transitions in Adobe Premiere Pro.
For a standard fade in and out, use Audio Transitions / Crossfade / Exponential Fade
Drag this effect to the start or end of an audio file / track. This is pretty rough and ready, but good for short transitions.
For more versatile and subtle control of audio transitions, fades and volume levels in Premiere set audio markers at transition points and then set levels between the markers. If you can’t see the volume levels on the audio file – right click audio file (in the main edit window) and ensure Show Clip Keyframes / Volume / is set to Level