Syntax is pretty simple:
mkvextract.exe tracks "D:\video.mkv" 1:"D:\track-1.aac"
D:\vide.mkv - Source file
1 - Track number ID
D:\track-1.aac - Destination file
mkvextract manual can be found here.
If you prefer to work with graphical interface, you can download a GUI add-on from here: https://sourceforge.net/projects/gmkvextractgui/