You need to use audio points. Just switch to the Timeline view and right-click your song. Then select Add Audio Point https://i.imgur.com/2BsJztq.png

Add a few points and drag them down to lower the music volume. In the end, you will have something like this for the fades: https://i.imgur.com/0cpGCn9.png

If you want to overlap two songs, add the second song to the Voice Comments track. Just right-click the track and select Add from file.

Thanks for any help!