I use Magix Music Maker to mix tracks together.
I used to create tracks using their sound pools - the software basically creates a track for you, and you can just tweak it.
Right now there's so much good music at Itch.io that's free or doesn't cost much that I haven't made my own music in years.
I mix the tracks, because they tend to be too short (the sounds become repetitive). Music Maker has great features to fade one song into another.